we were on holiday last week and at our hotel there was a girl of around 12 whose beach/swimming attire was a pair of bikini bottoms (i.e. no top). She had noticeable breast development. I was quite surprised by this, I think because my (slightly younger and less developed) DDs are starting to get body conscious and so would not be comfortable doing this. I don't think I felt disapproving when I thought about it (a 12 YO boy would only have trunks on) but was definitely surprised.
Just wondered what your reaction would be - have never considered myself to be prudish before!