Assuming that there is champagne or something available (it doesn't have to be at a university-hosted event, I can work around it, but I'd like it to be if possible), and the parents and the twenty-one-year-old are standing around drinking and laughing. 21 starts teasing the sixteen-year-old about being left out (it's his graduation, btw, he's a child prodigy). In Britain, it would be entirely plausible for one of the parents to say, "Well, two sips aren't going to turn him into an alcoholic." How likely is this to happen in America? (Background info: It's early 1990s, they're from California, they're currently in New Jersey, the parents are Baby Boomers, liberals, ex-war protesters and non-practising Jews. Mom's a lawyer, if that's likely to make a difference.)
I've Googled underage drinking + America, graduation, graduation + alcohol, but I' getting lots of 'don't let your kids do this' which is not what I want.