Some states changed it voluntarily before the feds came up with the highway funding idea though (Michigan, for one) The goal at that time was to get alcohol out of the schools because when one turned 18, they were most often still in high school. Then they could buy for all the 16 and 17 year olds. Now, it's 21 and the 21 year olds buy for the college students, but at least it's tougher for the 16 and 17 year olds to get it (although they still manage somehow).