There is no "normal" frequency of masturbation. You cannot "run out" of sperm (any more than you can "run out" of spit), so you can masturbate as often as you like. The worst thing that can happen is your penis might get a little sore. (Rub any part of your body that much and the same thing will happen!) In any group of healthy high-school- or college-age guys, some masturbate several times a day, some once a day, and some only once or twice a week or less. There are also a few who never masturbate – either because they don't have the urge, or because for whatever reason they have found a way (and a reason) to resist the urge. But for a young guy to be able to resist masturbating requires very strong will power – and frankly, we just don't see the point.