Is there a distinction between teenagers having sex and anyone over the magic age of 20?
I ask since presumably everyone does know that the majority of teenagers have regular sexual liaisons from way under 16 and all those that involve sex, which is a lot, are technically rapes. Yet many of those posting on these boards did the same themselves when young, and I doubt any feel they did anything at all wrong, or non-consensual, or took advantage.
That is why it is a very difficult area for the law. It is a blunt instrument and has to have a date cut-off point but as Mintball points out, no miracle occurs at midnight on your 16th birthday and there are many ready for sex much earlier, just as there are immature ingenues of 20 or more years, it all depends on both personality and environment.
In the context of a club, though, I'm not sure I see the point. If you were in adults-only club and felt you had to ask a girl if she was 16, I'd suggest you might be a tad unwise to pursue that one. Not least because if she says she is (and is hardly going to say no she isn't) it will not help your defence.
There will always be girls in clubs who are under age but absolutely don't look it or behave it, and frankly unless the young men in the club aren't looking for any action then there is nothing they can do but take that risk, since demanding photo-ID would not often be a winning chat-up line, I would guess. So yes, I agree, in that type of situation you 've little choice but to take things at face value.
But is underage girls in clubs a big problem? I hadn't heard so. I'd speculate that many thousands do turn up and get it, but that the vast majority aren't looking to get laid. Plus, after a few minutes of conversation, unless an underage girl had worked out an extremely good cover story and was a good liar, shouldn't a guy work it out anyway?