I was about to post an anecdote but had a recollection of posting it already. Looks like I did in this poll from several years back on similar topic of how comfortable people are naked.
As I get older I seem to care less and less. Different scenario than a single-sex locker room but I went to a clothing optional beach this summer for the first time. I was quite nervous at first but my 8 year old son and I joined the locals. It was actually quite nice to be swimming in the lake without a swimsuit. The crowd was quite varied in age from 20s through 70s (we were the only ones with kids there).