It has nothing to do w/ being mature or imature. Your endocrin system has not finished developing. If you flood your body with exogenous test you could seriously **** yourself up. Also, if your bf is at 4% you are dangerously low. I'm guessing that is not an accurate measurement. Get over in the diet section and post your diet. Read all the threads about bulking. Get your diet dialed in. You will get the gains you want from that.