I understand that some groups, (I think killing kittens might be one) vet applicants photographs and select attendees according to perceived hotness. Other groups have upper age limits.
The vast majority of clubs are open to all; younger, older, 10/10's, 2/10's, as they are, most commonly, non discriminatory and generally, most people aren't 10's in real life...
And ime, in many cases, visitors only have sexual contact with their partners, finding the location, the views, being watched, the whole experience, to be sufficiently exciting to float their boat. A friend of mine reckons it's actually a minority of club attendees that have sex with others and the majority do not. Again, ime, I'm not sure of the figures having not carried out detailed surveys, :) but you most definitely are not 'allocated' your partner(s) for the night. There is never ANY compunction or pressure on anybody to do anything they might not want to.
And as my DW always tells me, 'it's great as, for once, the women are in total charge.'' If a women says no, or declines an advance, thats it. We've been in regular clubs and she's been groped or aggressively hit on, this has never happened on our occasional swinger club visits as the offender would be told to leave. I've always found swingers clubs to be extremely respectful and polite, not a forceful free for all in any way.
We aren't in the UK any longer, but my two buddies who are still active on the UK scene tell me that Chameleons in the Midlands and LeBoudior near Heathrow are both jolly good fun.