Do you usually have to be 21 to go to a karaoke club/bar?

No, but it helps to sing karoake if you are drunk so . . . . . take your pick.

Underage and singing kaorake and looking foolish

or drunk and singing karoake, still looking foolish but no longer caring

18 to enter 21 to drink

No, just depends on where you go. Check out this karaoke site that my friend has:

http://www.harryoke.com/

Not really, but some place do restrict it to that age. It depends on the establishment.

someplace in my country 18 and some place even a 12 year old can go. lol

Most people do.. since you need to be drunk to do Karaoke.

YEP

nops...