I'm a mom, though not of a teenager. From what I hear from my sisters, they are aware that their sons do it, but aren't exactly having family discussions on the subject. If your parents are like most parents, they know you are the right age to masturbate, and probably assume you do. (Certainly your dad assumes it if he has any memory left of being 16 himself.) But if they are like most parents, they probably don't care to know any more detail than that. lol Not only because of the obvious eew factor, but also because they probably feel it's better to leave you your privacy and the dignity of being treated somewhat autonomously. (I did know one mom who got tired of washing sheets and blankets, and tossed her son a package of tube socks one day and said he should use those instead. That was pretty funny.)
2 - 4 times a day --- at 16 the hormone flows for a guy at that age are so wild, it isn't too surprising. As long as you are not cutting out other activities like school, sports and friends in order to be alone and masturbate, you're probably pretty normal.
This might be a better question for you to ask in the men's health forum - as a mom of teenage boys, I'm sure they do it but I have no idea the frequency.
I do see posts here about men who are dysfunctional sexually and they masturbate a lot - but it seems like maybe they're masturbating BECAUSE they're dysfunctional, not that they're dysfunctional because they masturbate.
I bet men would have more accurate information to give you than moms -
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