Not exactly, but there's no rule against it.

That's because they never had the mentality of Catholicism about sexual pleasure in general, never did anything to stop it (not even in the middle ages). I actually went once to a priest, I don't know how this is called in English, when you say to him all the things you consider bad that you've done, and told him about masturbation, and he said "It's normal, at your age, don't be afraid".

And on a teen forum I'm registered on, 90% of the users who voted in a poll (I could give a link but I don't want to advertise) did this before they were 16, so trying to stop it is not only stupid but also useless.