They used to say pro-tennis was a young man's game; Bjorn Borg dropping out at the tender age of twenty five, for example, after he lost a U.S. Open final to John McEnroe.
Drugs changed all that. Barrel-chested Agassi won more grand slam titles after his twenty ninth birthday than he did in his prime, winning them well into his thirties. He later confessed to doping, sort of.
Then of course there's David Ferrer, the near-miraculous Daveed, he who denies ever knowing Luis Garcia del Moral despite them both being associated with the same Valencian training academy; incredible stamina, big upper body development typical of steroids, Daveed finds overnight redemption in 2009/10 having fallen out the top twenty then surges into the world top five and stays there well after the age of thirty. The older he got the fitter he became. Laughable.
Now we have his compatriot, Feliciano Lopez, an ATP career playboy. He's just now reached a career-high world ranking of thirteen in his thirty fourth year.
http://www.atpworldtour.com/Tennis/Players/Top-Players/Feliciano-Lopez.aspx
Unreal.