I came from small town America and grew up in a much different time... Cops never really enforced the 21 thing (and girls could drink at 18) for beer, the whole town was German...
True story, late one night in the summer one of my Dad's friends, a local policeman pulls up next to us as we were sitting in the local burger drive in lot after it was closed, all 16-20 yrs old, sitting inside and outside our cars drinking beer. Anyway, Jack pulls up and sees me, motions for me to come over to his car, and say; "D@#$%^ hot out here, how about sharing one of them cold ones with me... So, I got him one and sat in the front seat of his squad drnking a beer with hime talking about hunting and stuff...
I had those swinging gimbal mounted wire basket like drink holders mounted in several places in my Ford Bronco!