That's just the age of consent for sex, but under 21 is legally underage for drinking. IDC about legal, I was discussing whether it was a good idea to have drinking with underage people present, meaning underage for drinking, but it's not my group, so have at it.
I personally won't be attending any of the functions where alcohol is being consumed, whether the attendees are closer to 8 or 80, but that's just me.