At 21 years old you are at your lifes peak of your own natural testosterone production, taking steroids will halt and completely shut down this natural production, and then you have 70% more chances of not recovering completely your testosterone once the natural production restarts.
It is dumb not to wait till your hpta mature IMO.
Read this:
http://forums.steroid.com/anabolic-s...-steroids.html
http://forums.steroid.com/anabolic-s...%2A%2A%2A.html