It's less than 2% of all adult males. I would guess that the peak age group for anabolic steroid use is ages 30-40 (that is, end-of-youth crisis not the youngest) but I'd be interested to know for sure.
Edit: government data says I am wrong. 25-29, apparently. But that's based on self-reporting so I do wonder.
Edit: government data says I am wrong. 25-29, apparently. But that's based on self-reporting so I do wonder.