be certain that after urination you wait long enough before leaving the toilet area to avoid some dripping. this has nothing to do with masturbation. and there is no "normal" amount of masturbation; many young men in their early 20's masturbate daily. this is not a problem in and of itself. if you continue with urinary leakage you might want to see your health care provider.
i am in my mid-twenties and masturbate four times a week. could this cause the dripping that occurs after i urinate?