Is mastubation bad for one's testicles.how much one can masturbate normally to avoid health risk.

You're fine: If you get really wild and your testicles are unsupported, they might get bumped around but i've not heard of serious injury. Essentially all men your age entertain themselves this way; you learn about your mind & body to prepare you for adult life & it helps you stay focused on other things. There's no physical danger; if you get an obsession, get with your doctor.