I think staying serious about any type of physical activity helps to keep a person young. Like Spatts said, there is a whole host of powerlifters in their golden years. Also, look at some of bodybuilding's greats from the past like Lee Haney, Robby Robinson, Dave Draper, Bill Pearl, Lee Apperson, I could go on and on and on. I think anybody who continues to push themselves, and who still trains with an intensity and fury not too far off from their competitive days, is gonna do well in the battle against age.
Personally, I am just a kid, I'm 24. My best years are way in front of me. But, I look at some of my friends, especially guys who I used to play ball with. 2 years after college, they stopped training, got fat, or got skinny and weak, just generally stopped caring. I see guys I went to high school with who stopped playing ball after high school and they went to hell in a hand basket weighted down by a brick. These are young guys, my age, who say "My knees hurt", "My back hurts", "I'm too old for that shit" (love that one). They act like old men, like at 24, their best years are behind them. I'll tell you what, if everybody physically peaked at age 19, we'd have one weak world. After college, I stayed intense, if you saw me train, you'd think I made my living off of it, I never backed off. I plan to take advantage of the next years of my life, my true prime. I want to get together with my friends when we're senior citezens while they're shitting themselves, I want to be the Bill Pearl or the Reg Park, the senior citizen who still trains like a beast, who still has 20" guns, who still has "it".
I think no matter what type of athlete you are, as long as you keep up your training at an elite level, you'll stay young.