Hmm, in 1969 while 18 years old, and while I was attending AIT at Fort Gordon, GA as an E-2 we could get served beer, not hard liquor, in the EM club, just not off base in Augusta.
We did sometimes drive the 20 miles to Aiken, SC where the drinking age was still 18.
Even at Fort Benning, GA you could not purchase booze at an EM club. They even have Georgia Alcohol Board members checking the clubs. When you enter the club, they stamped your wrist so that the waitress could see your ID card had been checked and you were 21 or over!! At Jackson, maybe the county had a law, I don’t know, but we could not get booze. I am from Alabama and you could not buy booze under age 21 here either back then. We always went to a guy that was a local bootlegger, who went to what in Alabama is called the ABC Store (Alabama Beverage Control Store). You had always pay him more for a couple of cans. I remember one of my buddies was always driving over to his house and getting beer. Everyone knew he was the guy to go too. He had two or three iceboxes full of beer to sell to mostly teens or some local drunks!!