Wow. I know the problem -- but I'm not sure it's a generational thing. I am an old guy and I am constantly amazed at the naked comfort of the guys at the gym (some young; some older). I ALWAYS wrap my towel around and always get my underwear on as fast as possible. There are guys (most younger than me, but maybe not exactly young) who stand in front of the mirror, shave, brush their teeth -- twenty minutes in front of the mirror buck naked. Then, as comfortable as if in their own bathroom, stroll over to the toilet for a sit down.
I try to get out of the locker room as quickly as possible.
Also, one guy (probably in his forties -- young, right?), who sits naked (bare butt) right on the bench in front of the lockers. This drives me crazy -- he sits there as he contemplates getting dressed. Of course I don't have the assertiveness in me to say something, but I always avoid the place where he sits (thankfully, he sits in the same place every day).
I doubt it's a generational thing -- just a personal culture thing. Some people are just more/less inhibitted. I'd be happy if more people were more inhibitted.
EDIT: -- I am not as old as EJA refers to in his post, so maybe there is something to the "greatest generation" being more comfortable without clothes in close quarters.