The laws on being 21 and drinking are actually really lax in the US. For example... every vacation I've been on since i was 16 I've been able to drink. In colorado for ski camp the liquor store at the bottom of the mountain sold to us, I was 17. Not to mention they sold to every other 17 year old there. In Montana I drank at two different bars at age 16. I looked young as fuck at age 16 too, no facial hair, although I am almost 6 feet tall and probalby weighed 180 around that time. For non-vacations the town 10 minutes away from me sells to us regularly, along with the other 16 year olds that have the balls to try (although I'm 18 now).
Thats just my take on the drinking age laws in the US. Although I have been denied a lot in MI.