In that case, said Tom Cecial, I was a madman of my own accord when I volunteered to become your squire, and, of my own accord, I'll leave off being one and go home. View in context
The 1984 National Minimum Drinking Age Act, [23 U.S.C. Â§ 158], requires that States prohibit persons under 21 years of age from purchasing or publicly possessing alcoholic beverages as a condition of receiving State highway funds.
How did we end up with a drinking age of 21? In short, because of the National Minimum Drinking Age Act of 1984. This law basically told states that they had to enact a minimum drinking age of 21 or lose up to 10 percent of their federal highway funding. Since that's serious coin, the states jumped into line fairly quickly.