Does over masterbation reduce testicle size , i'm 16 and have an erect length of 11cm and my testicles are the size of medium to large grapes?

No: Normal men, women, boys and girls masturbate (it's universal). It is not harmful, as the body goes through similar effects during regular sex with a partner (but too much of anything may become a problem). Masturbation does not stunt height, cause acne or hair loss, make you weak, create heart problems, lower testosterone, affect virginity, lower fertility, change your weight, or shrink testicles.