Conversly, when the drinking age was 21, the same 18 year olds, although still drinking, would have been more low key.
I was around thirty and still in barroom/night club mode when they lowered the age back in the seventies.
Suddenly the local high school football team was hanging out in front of the bathrooms, making nasty remarks to the women and elbowing all the men going to take a leak.
It took a couple of really great brawls before the kiddies got the message, but things did quiet down.
I guess you've just solved the problem of paedophilia, then. Just drop all laws against child molestation, and after a period where the paedophiles go a little wild, it should settle down to something more manageable.