Masturbation in excess could cause you to lose sensitivity of your penis but it will eventually return after awhile and you could lose interest in regular sex if you masturbate too often.
But other than that the only problem that masturbation in excess could cause is hurting your penis by making it hurt for awhile but it's not dangerous to masturbate too much.
Masturbate all you want but don't let it interfere with your life and take it over.