![Darren Cahill (left) and Gil Reyes worked together to keep Agassi at the top of his game. "After a tournament, Darren [Agassi's former coach] would often say: 'get him in the gym, because I see a different guy on the court when he's been in the gym,'" Reyes said.](http://cdn.cnn.com/cnnnext/dam/assets/121008090955-reyes-cahill-tennis-horizontal-large-gallery.jpg)
![Darren Cahill (left) and Gil Reyes worked together to keep Agassi at the top of his game. "After a tournament, Darren [Agassi's former coach] would often say: 'get him in the gym, because I see a different guy on the court when he's been in the gym,'" Reyes said.](http://www.cnn.com//cdn.cnn.com/cnnnext/dam/assets/121008090955-reyes-cahill-tennis-horizontal-large-gallery.jpg)
Story highlights
- Roger Federer continues to be a major force in the men's game despite his advancing years
- The Swiss champion heads a rankings list with 24 players over 30 in the top 100
- Andre Agassi's fitness coach Gil Reyes says modern game takes great toll on body
- Strength was a key factor in Agassi's longevity allowing him to play with "great relevance" up until age of 36
In a career already groaning under the weight of titles and accolades, Roger Federer joined another exclusive list of tennis luminaries when he beat Andy Murray in this year's Wimbledon final.
In notching up his seventh Wimbledon win a month before his 31st birthday, Federer became the oldest champion since Arthur Ashe in 1975, and only the 11th player in the Open era to win a grand slam in his 30s.
Only Andre Agassi (at the Australian Open in 2001 and 2003) and Pete Sampras (U.S. Open 2002) have achieved the feat this century suggesting that, more than ever, modern tennis is a game which favors the power, agility and the sheer exuberance of youth.
Despite the ambition of those young guns and not forgetting the distractions of a young family, Federer's desire to remain competitive appears undimmed.
After dispatching the then 23-year-old Juan Martin del Potro in the final of the ATP Tour event in Rotterdam last February, Federer said he hoped to be around for another "three, five, six years."
And following his silver medal at the Olympic tennis tournament in August he reiterated that wish.
"I'll be 35 in Rio. I think it's possible, but we'll see how it goes," Federer told CNN.
The Swiss champion isn't the only one enjoying a resurgence in the autumn of his career.
From his perch at the summit of the world rankings -- which he reclaimed after winning Wimbledon -- Federer surveys a top 100 in which almost a quarter (24) of players are over the age of 30.
Five places below the Swiss is Spain's David Ferrer (who turned 30 in February) while lower down lie Jarkko Nieminen from Finland and Austria's Jurgen Melzer.
The 31-year-olds, ranked 35 and 37 respectively, have both won tournaments this year -- the Finn winning the Apia International in Sydney in January while Melzer took the Memphis title the following month.
Germany's Tommy Haas, who turned 34 in April, is currently the oldest player in the top 25. The former world no.2, whose career has been plagued by injuries, started this season outside the top 200, but has shot up the rankings this year to a current high of 21 in the rankings.
The rise was helped, in part, by victory over Federer in the final of the ATP tournament on home soil in Halle last June.
"Maybe 30 is the new 20," the German told CNN's Open Court, not entirely in jest.
"You know, I think a lot of the guys are becoming so much more professional ... everybody is looking more at how physical the game has gotten and how important it is to stay healthy and fit," Haas said.
"Thirty, at the end of the day, is really just a number ... If you really love something and you want to do it the right way, why not do it until you really know you can't do it anymore."
It's a philosophy which Federer shares, Haas thinks.
"He's a world-class athlete. He knows exactly what he is doing. He prepares as well as anyone out there ... he doesn't second guess many things, so I'm not really surprised."
Gil Reyes, the feted long-time fitness coach (and friend) to Andre Agassi, says Federer is just a class apart.
"Roger is a perfect athlete -- his movement, his game, his mental, his physical. There's Roger and then there's everyone else," Reyes said.
Technological advances and the physically demanding nature of the modern game have caught up with players less gifted and younger than Federer, says Reyes, leading to lots of wear and tear.
Federer 'very proud' of silver medal 02:39
Haas on age: '30 is the new 20' 00:01
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With players hitting that ball harder than ever, there is simply less time to play the next shot, he says.
"You're going to be out of position unless you redirect your body very forcefully and very violently, and that's just taking its toll on our knees and our hips. So you have to counter that and prepare your body for the game," Reyes said.
Preparing his body for the game enabled Agassi to play with "great relevance" right up to age of 36, says Reyes.
The American's latter playing years were the most fruitful of his career with five of his eight grand slams won after his 29th birthday. He was also world no.1 at the age of 33.
"When you stop and think about it, that's amazing," Reyes says.
Strength was the key to Agassi's enduring success, Reyes believes, who recalls "a rather slender fellow" when they first met in 1989. But together they devised a fitness program tailored to the stresses and movements Agassi experienced on court.
"If we were doing certain running drills, he would say: 'I don't feel that on my legs the way I do on the tennis court.' That was beautiful because then he would leave it to me to come up with the training," Reyes said.
Reyes would also tailor gym work depending on the playing surface -- the high bounce at Roland Garros requiring different strength training to the skiddy low bounce of the All England Club's grass courts.
"I can say, honestly, that he was, if not the strongest player on the tour, one of the strongest. Playing to 36 in this day's game it takes a lot."
Reyes thinks the next generation of tennis stars will reap the benefits of improving sports science but does not envisage too many current players emulating Agassi, with one notable exception, perhaps.
At the start of the year, a back injury forced Federer out of the Qatar Open in Doha. It was only his second withdrawal during a tournament in his career and prompted speculation that 2012 might be a year of diminishing returns for the great champion.
Ten months on, Federer has a further six titles under his belt, and heads towards November's season-ending ATP World Tour Finals with just his own records as the oldest winner and six-time champion to beat.
