Idaho used to have a drinking age of 19. I’m not sure when it went into effect, but I believe they didn’t raise it until forced to by the feds. It was certainly at that age in the early 70s, when I went to college in a town only 8 miles from the Idaho border.
Wisconsin used to have split drinking age the same as Colorado’s, as described byInvisibleWombat upthread. This was in effect at least as far back as the 40s, if I recall what my mother told me about it, correctly.