John wasn't old enough to shotgun a beer. Did they really let him drink?

So today is John Cusack's 49th birthday and I've been binge watching most of his résumé over the weekend :) I got to looking up some of the titles on Wikipedia, and in one paragraph it says that he was 16 during production. First of all, if he was 16 (b. 28/6/1966), that puts the filming around 1982-83, and the movie didn't come out until 1985, so I'm wondering why the 2.5-3 year delay?

Second, I'm wondering if they really allowed him to drink all that alcohol that Gib consumes throughout the movie. He shotguns the beer, he guzzles whatever liquor is in his dorm room, he has wine at dinner, he drinks that strong stuff in Lance's room... Gib's got a hell of a constitution, but the guy playing him isn't old enough to be so grizzled yet!

In US, the drinking age was 18 until 1984, when it was raised to 21. So that would mean that even if they finished shooting in 1985, John would have barely missed the cut-off date and wouldn't be eligible to drink until June of 1987. Plus, the bartender even asks Gib if he's 21 (not 18), and of course Gib provides a fake ID of "Dr. Levenson". But if John was only 16, that's way too young to be having any alcohol.

Isn't there some kind of liability the production company could have faced, letting a minor drink alcohol on the set? Unless they did filming in Canada, where to the best of my knowledge the legal drinking age is still 18. Or they gave him fruit punch or soda, and empty beer cans otherwise. Or unless there's an implicit rule that Hollywood just looks the other way...