Sometimes i see loads of cut guys in the gym, and sometimes everyone is uncut but I think it’s all down to where the guy is from.
African, Arab, Pakistani and Bengali guys are cut.
British, Eastern European and other white guys, Caribbean and Indian guys are usually all uncut.
With white guys it seems the older they are, the more likely they are cut. Maybe it was common in the UK to get cut back then as i see a lot of white British guys 50+ who are cut. Anyone below that age is usually uncut though.
That does bear out my limited experience. In the nude swim club I belong to, the members are all UK (we are in a very rural area), and there is a high percentage of circumcised men, and most of them are over 50. I have no idea why any were done - it's not a topic that comes up! - but there are some 30-50 who are, and one who usually has his foreskin retracted. As @Lad1995 says, some meetings can be all foreskins (well, except mine!), and others all circumcised.