Actually, in 1984, Congress passed the National Minimum Drinking Age Act, which required states to raise their ages for purchase and public possession to 21 by October 1986 or lose 10% of their federal highway funds.
Maryland raised the age in 1984 (from 18 for Beer & Wine) but Grandfathered anyone already allowed under the previous law (I was one of them, so I remember it well!)
Interestingly, DC did not raise the Age until 1986 ...
I was legal in 1984, 1985, and 1987 (NYS went from 18 to 19 for a year, then that year to 21, without grandfathering).