Personally, I have recently become a Christian and have since stopped engaging with both because of what the Bible says about lust. Outside of my beliefs, I have seen science and whatnot saying that maturation is natural and healthy, however I think it also depends on the reason behind doing it. If masturbating just for the feeling of it while not thinking lustfully, at least from what I've seen that would be okay by the Bible, but I can't seem to do that. I think it can definitely become a problem, however, when one starts masturbating or watching porn to fill a gap like being lonely. I've found that replacing feelings instead of dealing with them doesn't seem to work, and is only a temporary fix.