Well lets lay it out plain and simple then ,at 21 he is just easing out of puberty,still in my opinion 21 is still young, But he has fresh receptors ,you can de-sentized them running too much,not to mention raising your LDH/HDL Cholorsetrol levels,this will lead to cardiovascular problems as he gets older,not to mention the sex drive of a 70 yr old.
Less is better-not more,I guess some think that they won't have to train as hard on AAS(FALSE) You reap what you sow.