As a memebr of particular "generation" I feel more at ease participating at an event where the guidelines makes it attractive for me to attend or in the inverse politely suggest that it may not be my cup of tea (no relation to the royal wedding). It would be like the doggy owners club meeting and to have some prat show up with a cat, which would only spoil the meetup for the dogs and the poor cat.
So whether the guideline is +35, ladies only, under 30's, men over 1m85 (for the tall ladies), etc we should respect the invitee's guestlist wish so that his/her event is a success. If one can't respect that, then organise your own event catering to your own ideals.