I will say this, however the typical seditary American lifestyle doesn't help matters. I think if you're a health nut and exercise regularly, that age range can extend maybe 5 years at most, but you'll eventually see decline. Mostly hormonal stuff that effects the entire body, that's just how the cookie crumbles.This is classic but goodie Sage. I would say between the age of 25-35. For athletes its a combination of physical performance and experience.
After 40 and I don't care what kind of shape you're in, your body will break down sooner or later. Old injuries will eventually resurface. You will start to slow down and you will become more brittle. Even if you work out and you're a health nut, father time always wins.