What do you think about the drinking age being 21 here but 18 in the rest of the world?

I'm not asking because I'm not 21 and I can't drink, I'm seriously curious. I just don't understand how in Europe and everywhere else it's 18 but it's not even enforced, so 14 year olds can drink alcohol. In Canada which is right next to us it's 19, so what's the point of making it 21? I just think it's dumb. For example at the college I go to, one night 3 young women were raped and where were the police? Nowhere to be found because they were too busy busting parties where people were just having fun and not causing any problems. Like really what is the big deal? People have to be arrested over drinking some alcohol? I just think police should concentrate on things that are far more important than ruining some teenage fun and I think it's an absolute disgrace that they weren't there when the women were raped. This is just my opinion but I just don't understand why it's 21 here and 18 everywhere else. What do you think?