Depends where you live. Plenty of American towns have parks and beaches. Sadly, many of these places ban alcohol (which also makes no sense). Allow alcohol in these places (with strict rules against littering) and that creates public spaces for drinking. Americans are funny in that a man drinking beer in the park scares many the homosexual agenda or invading foreign nations is cool with the same people (I know I am overthinking again).The thing about drinking under 21 in usa is that people never socialize at home and there is essentially zero social public space for youth to hang out as in Europe (parks, squares, river banks , etc) on top of accessible public transportation.
So for these reasons I'm against setting age of drinking to 16.
Moreover if people-across all ages have no place to socialize, then teens are more liable to drink often. After all the boredom is why people drink, smoke weed, watch porn, play video games and watch entertainment far more than anywhere else in the world.
Also, I think many Americans socialize regularly at home. Barbeques are very popular and so are movie/game nights. Drinking at bars is extremely expensive to do on a regular basis for those lacking good jobs.