A drinking age of 21 is too high. A drinking age of 18 may to low. Lowering the age to 19 makes the most sense. While a temporary culture shock would ensue for a few years, America's young adults would become as responsible as Britain's youth or any other sub-20 year old law countries.
http://www2.potsdam.edu/hansondj/YouthIssues/1046348192.html