User: jamesbreitbart
Two, a brother and sister. I didn't really need to convince my parents, they just decided I was old enough to take over baby-sitting duties.
I had babysitters until I was about ten or so, after which I was responsible for watching my younger siblings when my parents went out. Obviously it depends on the individual child, but I think a single child should usually be able to be responsible for themselves around age 8.
I like skinny-dipping, but I don't think it should be mandatory. If people are forced to do it, especially in the teenage years, then they'll develop a negative association with it.
When I was a kid 10 or so years ago it was pretty common for boys to play outside shirtless in summer, and you wouldn't bother putting a shirt on if you had to make a quick trip to the store or something.
My family does nude present-openings, but sometimes I'll wear a santa hat to be festive.