This has all been very interesting!

At the Y I use, we have shower stalls with curtains, and the norm is to wear at least a towel while walking around. A few change in the toilet stalls, but most of us are at the lockers, making some efforts towards modesty (facing the wall while putting on underwear/bra). However, there are quite a few older women who do walk around naked. It's kind of wonderful, how comfortable they are in their own skin.