It's to do with the scientists at american universities. Their research implies that the human brain isn't fully developed until at least age 20 and that alcohol is most damaging before that age, and given the proximity to our legal system, they've got the level of influence to impose the research. Not like it matters that much. Besides, if someone younger than 21 wants to drink that bad, they'll find a way.
Yes. but the laws are just weird
"I'm old enough to make legal porn but I'm too young to drink beer"
