Also my local gym is very popular with the 50+ crowd. There seems to be a large social aspect to it for them. Don’t knock it!
I can say that around here in downtown-ish Bucharest the annual subscription for a popular gym varies between 500 to 800 euros per yer, depending on the chosen plan/options, but you really do want to get the more expensive plans/options that are between 700-800 euros. That is if you pay all in advance, if you pay month by month or 3-months by 3-months (it's all so complicated) the costs are between 80 to 100 euros per month.
I agree though that all this may vary. As a man you may choose to "cheapen out" a little and choose less expensive gyms that are located further out or who attract a different kind of clientele, but that option may not be available for many women (as my partner is), unfortunately.
Going to the gym is also not cheap, and, even so, we're not all late 20s - early 30s people, us people in our 40s or in our 50s also need a nice place to hang out without getting physically exhausted in the process.
As for the hobbies, most of the "community" ones also require relatively more money to be spent, and, again, it pertains to a certain demographic.