Why is legal drinking age 21?

Answer 1

Because Congress passed and former Ronald Reagan signed The National Minimum Drinking Age Act of 1984.  The bill is drafted so that it skirts the 10th amendment of the US Constitution bill of rights.  Each state has the right to set their own drinking age, the federal government does not have the right to make the state chose a drinking age because of the 10th amendment.  The National Minimum Drinking Age Act of 1984 works around the 10th amendment by not telling states they must make the drinking age 21 but by telling the states that if they don't make the drinking age 21 then the states will lose a large percentage of their federal highway funds.  So this is how the federal government skirted the constitution to make the states do what they want, they do this with all sorts of issues.