How old on average are people at nightclubs in europe?

Certainly in the UK it's an under-18s that normally shuts at about 11pm(no alcohol, although they are invariably pi$$ed anyway) to let in the over-18s(alcohol served). I've never heard of anyone over 18yo trying to get into an under-18s, it's always the other way around. But he's right in what he says by most folk tend to stop going to clubs(not so much bars) by their early/mid-20s here. It just gets very boring!