Bolt was fast when he was 10 years old, and probably was still naturally fast when he was 21. After any injuries though, it's likely he started peds.

I was the strongest man in one of the Bay Area gyms for a while, all natural, but essentially that was the focus of my day for several years while I worked at home (next door to the gym) and I had 10 hours of sleep nitely.

I went to a natural bobybulding conference once and all the pros were staring at me - I was huge. So it can be done while you're young, but under perfect conditions and until you get injured.