One reason I like the Rock is he seems very aware that he's a role model for young boys, and he takes that responsibility seriously. Lying in this case is perfectly appropriate. Telling the truth would encourage even more teenagers to do AS without knowing what the hell they're doing.
The growth-stunting issue aside, AS are serious drugs with serious dangers and side effects and teenagers are frankly not prudent or responsible enough to mess around with them. (I know I wasn't, at sixteen. Thank God I didn't have access at the time.)