In Australia, It's 18 for everything. Voting, Drivers License, and drinking
Works well, but I think you'd find that dropping the age in the US to 18 will see a lot of "nearly 18's" drinking a lot more.
Also the BAC limit for new (18yo) drivers here is 0.00% for the first 3 years. So that limits them a bit until they are 21 anyway.
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