The legal drinking age in all states is currently 21, courtesy of a federal highway grant which removes a large amount of funding when a state changes the legal drinking age.
An age of 19 would keep it out of high schools.
As can be seen on college campuses around America, this does not prevent the majority of people aged 19-20 from drinking, but rather forces it underground where it is more difficult for police and health care professionals to help regulate, which increases alcohol-related health issues.
Health issues aside, there are a lot of legal implications for college students; many students drink and many of those students want to be able to purchase alcohol, so they get a fake ID. When caught, both of these actions have serious, lasting legal reprecussions, often undeserved