The boy is now a man. Joseph O’Brien was thrust into the spotlight as little more than a child, the 16-year-old son of a genius trainer, and displayed tremendous riding acumen from the start.

He was 21 eight days ago and in the intervening period has been champion apprentice twice and champion jockey the last two years.

Although his uncle, Pat Smullen, will have something to say about it, you wouldn’t bet against him making it three on the spin.

In keeping with his father’s trend, he has broken plenty of records, including the number of winners by an apprentice (57) and a fully-fledged jockey (126) in a season.

There have been new marks set by virtue of his youth in a variety of prized races. The tag of him and Aidan being the first father-and-son jockey-trainer combination to win the Investec Derby with Camelot in 2012 is particularly satisfactory.

He was just short of his 18th birthday when winning his first classic, the Irish 2000 Guineas, on Roderic O’Connor. A few months later, he became the youngest victorious jockey in Breeders’ Cup history.

To date, he has six classics to his name and next Saturday, Australia will be hot favourite to provide him with a seventh in the blue riband of European flat racing.

One can only imagine how difficult it is as an adolescent to have your every move analysed, to be glorified one minute, the subject of some vitriolic criticism the next.

O’Brien has had to grow up quickly but last Tuesday, as he stepped out of his jeep with a smile and shook hands, before leading the way through the Giant’s Causeway yard at Ballydoyle which houses most of the star pupils, it became clear that he has come through the process very well.

That’s a credit to his parents no doubt, but mostly the young man himself. He remains humble, quiet-spoken and gracious. When the matter of his weight comes up, he admits being embarrassed it gets such publicity, given that many other jockeys are making similar or worse sacrifices without having rides on Derby favourites to motivate them.

Bottom line - or “the long and the short of it” as he likes to say himself - is that Joseph O’Brien loves riding horses, and knows he has been granted an incredible opportunity to have the best thoroughbred talent on the planet at his disposal. While understanding that some might use this fortune as a stick to beat him with, to belittle his own ability, he just cannot see any reason to complain.

He is almost a clone of Aidan, even starting many of his sentences with the word “Listen”. And like his father, Joseph has become more comfortable with the media. He is certainly pretty chilled after a morning’s work in glorious sunshine.

“You spend the winter with the horses, tipping away and keeping things ticking over, looking forward to the summer,” smiles O’Brien junior. “Then you’re looking forward to getting stuck into it, getting into the big races, the big days, the big meetings.”

Ballydoyle has produced 10 Derby victors, with its initial master, Vincent O’Brien providing six. Aidan is looking to add another line to his lengthy CV by becoming the first trainer to complete a three-in-a-row in the Epsom centrepiece.

“The Derby can make a horse’s career. It’s a massive race and it takes a horse that has everything; they have to be balanced, have to have the pace and have to be able to stay. It’s the ultimate test of horse and jockey. It’s one of the biggest races of the year for us anyway.”

Australia is considered by many to be unbeatable. Joseph would never say that, despite his father lauding the horse as his best ever, with the exception of three-in-a-row Champion Hurdle victor, Istabraq. You can sense the confidence though.

“We were delighted with him (in the 2000 Guineas, when he finished third). Obviously when you don’t win you’re always a shade disappointed but he ran a massive race. It’s all systems go for the Derby and hopefully stepping up in trip will suit him.

“He’s loads of pace but you’d imagine that he will improve for the step up in trip being by a Derby winner and out of an Oaks winner. I’d have no problem going back to a mile with him but you’d be hoping he’d be even better going further.

“We’ve done enough talking about the horse. Hopefully he can show on the track on Derby day and the rest of the season what he’s been showing us at home for so long. I suppose it’ll be the first time he gets the chance to show it.

“He was very green first time out and ran a lovely race, won easy second time, won easy the next time in Leopardstown, and he was just touched off in a Guineas. So he’ll be going a mile and a half now, hopefully we’ll get a clear run, an uncomplicated trip and after that then, he can do the talking.”

According to O’Brien, “Dad’s eye” picked Australia out as special early on. The son of Galileo gave a different feel when you sat on him. Then he started doing things like going half-speed with older horses and treating it like a morning stroll; running four consecutive furlongs at 11 seconds a furlong.

A good attitude is one of his best attributes though. Relaxed, laidback, unfazed by anything going on around him. O’Brien tells you this and he could almost be talking about himself. You say that and he bats it off, just lucky to be in the position he is in, “riding the biggest races and the best horses”.

But it’s not that straightforward. Yeah, he got a good start, but he had to have talent. He had to be dedicated. Does anyone really think Aidan would have put his 17-year-old son on Roderic O’Connor if he didn’t think he was up to the job?

There is too much at stake in this huge business that goes way beyond training horses, for him to even consider making such an emotional call.

Of course, the decision was completely vindicated by the brilliant judgement of pace Joseph produced from the front at the Curragh. To the uninitiated, it looks routine but of course it’s not. It’s how many view his career. Easy. It’s clueless but that doesn’t stop them sticking the boot in.

“I often have to delete Twitter off my phone ‘cos it just goes mad when you don’t win on a favourite and different things like that. But I suppose that’s part of the job. When I was younger it did not get to you, but you’d be a little bit sickened over it. But I’ve developed a bit of a thick skin at this stage.”

You don’t have much choice when your friends are entering your name in Twitter and reading out some of the more insane stuff, just in case you’d miss out. He’s laughing at the memory of the tough love.

“I’m usually hard on myself after races anyway. Every race that any jockey doesn’t win, they’d do something different if they could have it again. If you don’t win, you want to do something different to try to improve, to try to win.

“But everyone is entitled to their opinion and they’re able to get it to you fairly quick on Twitter! That’s the long and the short of it… but I don’t mind it.”

A lot of it is about people not understanding. John Gosden was refreshingly honest minutes before the Irish 2000 Guineas when he said that James Doyle had been instructed not to knock Kingman about in the ground if the race wasn’t there to be won. Connections have a duty to a horse’s welfare, and the longer term.

“You want to win today but it’s a bigger picture. You want to win every race but sometimes the bigger picture means you ride a horse a certain way. You always still hope that you can win the race doing that but it’s not riding the horse much different, it’s finding how they like to be ridden.

“Sometimes the race works out for you and sometimes it works out against you. And like I say, every time you don’t cross the line first, you want to do something different.”

He feels bad that sometimes he takes growing up in such a monument to thoroughbred greatness for granted. Whereas outsiders get goose bumps just driving past the Nijinsky statue, thinking about Vincent O’Brien, Lester Piggott, Pat Eddery, El Gran Senor, Sir Ivor and Sadler’s Wells.

There are reminders everywhere, though, and on occasion, he looks at a photo or painting and it dawns on him all over again.

But this is home, and has been since he was four. All he has ever known is horses. He played soccer, football and rugby in Rosegreen and Rockwell but was too weak. It didn’t bother him. He was always biding his time.

He was allowed ride work at 11 and meantime, developed his horsemanship in pony eventing. He won an individual bronze medal at the European Pony Eventing Championships in 2009 on Ice Cool Bailey. The legendary Connemara pony subsequently steered Sarah and Ana to similar finishes, while Donnacha surpassed them last year with a team gold and individual bronze.

You wonder if they talk about anything else around the dinner table.

“People laugh at you and they don’t believe it, but not really!” He laughs himself. “That’s the truth. You have to relax a bit at times as well but I suppose it’s our life.”

He was a fan of Breaking Bad and watches a few similar TV series. The family generally goes on a holiday - usually to Barbados - after the Breeders’ Cup. Joseph and Aidan play some golf. “Very bad” golf it seems. Apart from that, it’s winter with the yearlings, and summer racing.

It’s a passion, “second nature”, but surely, when friends are heading off travelling and getting up to mischief in somebody else’s back garden, the prospect of doing likewise must hold some appeal?

“You’d sit down and think about it but after two days your head would be melted and you’d just want to get back riding out.”

It’s just not him. Anyway, why would you want to give up a day like the Breeders’ Cup and St Nicholas Abbey, the entire family there with beaming smiles and a few tears? One of the best days.

“Definitely. The Breeders’ Cup is the world stage and it’s very hard to get a winner there. To have a ride there was unbelievable and when he won, it was a dream. I could never have expected it to happen. When you do something like that once, it’s like a drug and you want to do it again.”

The English St Leger in 2012 was at the polar opposite end of the emotional spectrum, however. Camelot was going for the Triple Crown but just couldn’t pick up Encke in the final furlong and a half.

Joseph was gutted, for the horse more than anything. Watching Aidan lead horse and jockey in after, you could see he was trying to protect his son. He knew what was coming down the tracks.

“It was sickening. But what can you do? It’s horseracing,” says Joseph now of the result.

“If I had the race again I probably would have rode him handier in hindsight. But if I didn’t have hindsight, I’d have done the very same thing again. And I rode him the exact same as I rode him in every race that he ever ran in. The race worked out to plan and we were a bit unlucky on the day I suppose. But it was pretty sickening.”

The worst day?

“Yeah.”

It’s still tough to talk about but the men who helped him and moulded him along the way, such as Kieren Fallon, Johnny Murtagh, Seamie Heffernan, Colm O’Donoghue and the aforementioned uncle Pat have had bad times too. You deal with it or do something else.

It’s funny to think now of O’Brien once being too small to play any contact sports. He’s as good as six feet tall. Get him on a good weights programme and he’d be just what you were looking for.

It’s completely the wrong height to be a flat jockey though. So he watches what he eats, although he’s not torturing himself. Two chocolate biscuits are munched over tea and he is looking forward to a “proper dinner” later on.

“I keep fit and eat well. Obviously when I’m doing light, I keep an eye on it for a day or two, or however long I have to. I’d have 9st, once or twice, or maybe three times a week, apart from the big meetings. So I’d have a couple of days where I wouldn’t have to go mad sweating or wasting.

“So it’s just keeping yourself fit, healthy and not to kill yourself on the days you don’t have, and when you have to take off a bit of weight, go for a run, a hot bath and you can take off a pound in the sauna when you get to the races if you have to.

“I think it’s great to be able to do it. People are always asking me about my weight but there’s jockeys doing it every day of the week to ride horses half as good as I get to ride. I get a bit embarrassed sometimes people asking me, because of that.”

The five-a-side astroturf game with some of the stable staff helps too, although you imagine sliding tackles aren’t allowed. He doesn’t expect to be able to keep going, he says, but you get a feeling that he is just steeling himself for that eventuality. A part of him is hoping he can go on for some time yet.

“Realistically, I probably won’t. But I’ll keep at it as long as I can. If that’s 10 years, 20 years or a year, so be it. But my weight is very similar to what it has been for the last couple of years and as long as it stays like that I’ll stay riding. I’ll stay riding for as long as I can.”

An article in a national daily newspaper in 2011 said he was on borrowed time. It has been pretty much the same story since, and with his father housing some National Hunt horses of late, the rumour mill is suggesting that the way is being readied for Joseph’s training career. Because he definitely won’t ride over jumps, they say. Wrong.

“I hear it every year myself. My agent, Kevin (O’Ryan) rings me nearly every year, come the back end of the year ‘well, I heard you’re retiring again’. I just start laughing.

“I will ride over jumps but I don’t think I’ll be a jump jockey. I’ll definitely have a couple of rides over jumps. I’d love to do it for the enjoyment of it as much as anything. But it’s a tough game.”

The NH horses were for Sarah, Ana and now Donnacha (who will be getting his licence just before Galway) to ride in bumpers. The older brother is proud but he’s particularly looking forward to Donnacha hitting the track.

“He’s given me plenty of stick over the years so I can’t wait until he messes up on one!” he joshes, the wide grin that has been in regular evidence, beaming forth once more.

So you bring him back to Epsom. The Best Your Father Has Ever Trained. That’s big pressure.

“I think pressure is a good thing. The more pressure you’re under, that means you’ve a real good chance of winning. You must be riding the favourite or second favourite. I think it brings the best out of people. It’s there and you feel it but there’s nothing you can do about it and you can’t let it get in the way of doing your job. I love being under pressure.”

Ground conditions allowing - “I don’t think he’ll ever race on ground any slower than good” - Australia should win.

“It is a big statement but he is a 4/6 shot, or whatever price he is. I think he’s a very good horse. He’d a very good run in the Guineas. All going well, with a clean trip around, if he can do himself justice and show what he’s shown at home, hopefully he can run a massive race and I’m really looking forward to it.”