My daughter left at 21 then they raised the age limit and she rejoined and there was a great competition at the championships last year where you did show jumping then went on to xc fences. She won it and won some lovely prizes and a beautiful trophy [which has to go back for this years winner ,she is now too old again]
Why don't you contact the DC or secretary and explain why you want to join. If they were going to be any good as a way of meeting people they should at least come back with some names or an invite to a couple of rallies to have a look - even if you can't actually be a Pony Club Member.