It seems like your problem may have to do with religious/social guilt rather than any real medical problem. I am a woman who has been masturbating since childhood. It helped me with stress and I am now married with an active and healthy sex life and I still masturbate on occasion.
Some studies have shown that regular masturbation is beneficial to blood flow and keeps the sexual apparatus in good health. Masturbation is also great for practicing arousal. If you are feeling guilty for religious reasons, then by all means talk with your priest/pastor/spiritual leader, but there is absolutely no medical reason to stop masturbating unless it interferes with your normal life in some way (i.e. masturbating in public, or masturbating so frequently that you do not do other things, like eat). These cases are also a mental health issue and not directly related to the physical act.
Stop worrying - nothing wrong with masturbating at age 20.
You seem quite distressed about this. Why? There is nothing wrong with masturbation. Are you hurting anyone when you do it? Are you having perverse fantasies with it involving youguns? Are you married and find it hard to perform for your wife because you'd rather masturbate? Then don't be so hard on yourself. You're not a freak. It isn't despicable. It is simply human nature that just so happens to feel pleasurable.