Im twelve, but I can still do great. Really, there is no age limit, it's more of a maturity thing. I can easily keep up with 3 sets of 25 PushUps 5 PullUps 50 lunges, each side, 50 squats, repeated three times a day.
It really depends if your actually going to work at it, regardless of what other people think.
(I remember one time, a bunch of older guys saw me vaulting, saddle vault since that was one of the two vaults I knew when starting out. They came over, made fun of me, I later left towards a nearby creek. A few minutes later, they follow. After hiding, they found me. Again. after leaving, I noticed my watch was missing. Next time I see them, Im toatally going to backflip his face off...)