By comparison, the average English Channel swimmer is 31 years old.

"Open-water swimming is so much more exhilarating and fun, so much more aggressive," says a wide-eyed Styles, a Singaporean-Australian student in year nine at the Australian International School (AISHK).

Chau, a swimming scholar in year 10 at Harrow International School, explains the appeal with a grin: "There are no lanes and there are no rules - everyone's crashing into each other and it's a free-for-all."

For Kelleher, another AISHK student in year 11 from Australia, it's an escape from the drudgery of "following the black line" for hours on end. "I can't stand pool swimming - you go up and down and the precision is so specific," he says. "I'd prefer to get out there, get in the open water and fight for it."

Their enthusiasm belies the talent they possess. "There's always been a tenacity to Neeks," says Kevin Styles of his daughter, Aneekah. "For a quiet little girl, I've always been amazed by that aggressive side which stands up in the ocean."

"I do get worried," adds Tim Kelleher, Angus' dad. "Even though he has a lot of ability I always say, 'respect where you're going, what you're doing, safety first'."

Chau adds: "You need to be tough and really competitive … some people can't cope with the waves and the current. Often it's freezing cold … you really have to be able to endure, otherwise you have to give up."

The trio is a small sample of top young local athletes making the fearless transition from the pool to the ocean. It's leading many to question whether Hong Kong's Olympic potential in marathon swimming has been fully considered.

"Hong Kong definitely has the potential to produce world-class open-water marathon swimmers," says swimming coach Lloyd McBean, founder of the Open Water Swimmers of Hong Kong.

"It has the right ingredients to be a dream training ground, given all the 50-metre pools and great beaches from Clear Water Bay down to the south side of Hong Kong Island.

"It has a great climate all year round for swimming in the ocean, its beaches and bays don't get big swells, waves or currents and they are shark-free. Conditions are normally flat waters - perfect for open-water training."

Chau certainly hopes so. By the end of the year he aims to be the overall long-distance swimming champion and after that, the Olympics.

"It will take a few years to improve to the next level, but [the Olympics] is definitely my goal," he says.

Since a 10km open-water swim was added at the 2008 Beijing Olympics, the sport has enjoyed a surge of interest globally. "It used to be just a sport for the older swimmers, but we've noticed many young swimmers coming up through the ranks recently, taking all the top spots," observes McBean.

Given their training, the success of Hong Kong's youngsters is no surprise. Styles trains up to eight times a week for up to two hours; Chau trains twice a day, most days. Even Kelleher, who has pared back his training for his studies, trains five times a week for hours at a time.

"They're training really hard and are incredibly fit, they just go like rockets in the water," says Dr Kenneth Thorley, the AISHK swim coach who recently retired from his post.

"The only thing holding these kids back would be fear or inexperience," he says. "We do see a lot of kids who are really incredible pool swimmers but some just refuse to get in the water."

Despite McBean's belief in the potential to develop braver young athletes, he has his doubts about the city's ability to deliver on the dream.

"Hong Kong has so much potential to produce elite open-water swimmers, but," he shakes his head, "I just can't see it happening. So many kids just drop out."

Natasha Tang Wing-yung was the first and only Hong Kong long-distance swimmer to go to the Olympics in London in 2012, where she finished 20th out of 22 swimmers.

McBean cites the lack of the support at an organisational level.

"These kids really need to leave and complete their training in Europe, US or Australia, if they want to reach elite level."

His comments echo the criticism from swimming star Geoff Cheah of the Hong Kong Swimming Association for holding back its athletes last year.

Kelleher started swimming in the open water aged six as a "nipper" (young surf life savers) in Sydney, yet attributes his rapid improvement to his experience in Hong Kong's waters.

But it's a double-edged sword, says father Tim: "Being here's fantastic. Angus has really developed and his times qualify him for the Australian National Open Water swimming team, but we can't get him back because competitions are during school time."

For now, he's enjoying the burgeoning local racing scene, though he's concerned a clampdown by the Leisure and Cultural services Department on issuing race permits may stifle competition.

"It would be a shame to see competition reduced; bigger competition is not only more fun but helps to really test yourself."

Chau also admits his niche sport could do with extra support, saying it gets "a little lonely" at times. "I think if we want to take it to the next level we need to join in around the world and gain more experience, socialise more."

Kevin Styles has observed that "many coaches hate the open water - it's a different technique ... so there's not a great deal of enthusiasm for it".

Irrespective of the outcome, Thorley believes the trials of open water set his charges up for life.

"Swimming training itself develops perseverance in these kids, then being able to go out there and challenge themselves against the elements, where they can't see below them and don't know what's going on. That really develops mental toughness."

"If more Hong Kong kids were to take part in the sport I think they would break down that barrier of 'I can't'," says Kelleher. "If you step outside your comfort zone a little bit, I think you'd surprise yourself."