I can't remember ever getting asked for ID here when clubbing. I did always look older than I was and a lot of the people I went with were older too so I kind of got in the middle of them on the way in
When I was in the States it was a pain as I was 20 and they card you EVERYWHERE there. I turned 21 whilst I was there but used to use my International Driving Licence as ID and that fooled them into thinking I turned 21 a couple of months before I did as they read my birthday as 3rd January instead of 1st March due to the inverted way they write dates