Skinny dipping was something I did a few times, when I was that sort of age, so I don’t understand why the prudishness, either!
I have some very funny memories of such times. One time, on holiday, a female friend and I went skinny-dipping with our boyfriends, got out before they did, stole their clothes, ran off (keeping our flip-flops off and running back in our bare feet, so that they couldn’t catch up with us!), leaving them to walk back to the house we were staying in, naked, locking them out for a bit when they got back, for good measure!
Fun times!