I started gliding with a week long course at Challock aged 17 then from 18-21 at a small club then 21-25 at Dunstable. I loved Dunstable and never though about age but I guess most were older. It more came down to hours experience and X Country distances etc rather than age as to who you mix with.
I then got a UK PPL after a Silver C conversion in just 16 hours instead of 40 which was a big saving, before going onto CPL/IR. In spending a day at a club you learn other skills like driving and repairing tractors, driving the winch and rigging/derigging gliders especially when you get into a syndicate. These make the day go quick. At Dunstable you can stay for a few days or weeks intense gliding if you dont want to commute, or at least you could when I was there.
Because its got winch launching and a ridge these keep costs down as you can get plenty of airtime. I had years of winch launching and never got less than a 30min flight with ridge, thermal and weak evening wave lift. Even cross country flights can be started with a winch to the ridge.