The hypocrisy appears when they don't pass the same judgement on themselves. Do they disapprove of what they did when they were younger, or do they think "oh, well that was all fun and games, but these kids should not be drinking"?
I had this discussion with my mother (who went to school in the early 70s) when I entered school. Her position boiled down to it being reasonable for her to drink because it was legal, and unreasonable for me to drink simply because it was illegal. Now, I don't equate legality to morality, in no small part because she didn't raise me to do that. When pressed to actually explain her disapproval, she relented and admitted that her position was hypocritical.
Hypocrisy isn't about changing your mind. It is about holding yourself to a different standard.
I don't interpret that as hypocritical. Whether legality equates to morality doesn't matter. If you get caught, there can be serious consequences (legal penalties, kicked out of schools, etc.. all depending of course on the circumstances of the party, the party-goers, the school, the state, etc.). These risks didn't exist when she drink in college. They do now, and it's not unreasonable for a parent to want to prevent these things from happening to their child. Their opinion can be 0% percent judgement based (in the sense of "passing judgement".
I think we both knew that, in practice, there is no real risk in being kicked out of school for hitting up a party on Fridays so long as you act with some baseline level of responsibility. In my case it wasn't even a dry campus (and few people other than freshmen were in school housing anyway, so the parties were on private property), and nobody had cars (campus was in the city). In this specific case, her judgement was based on mixing the legal and moral signals, but she does not normally buy into that.
I would describe her position at the time as slightly hypocritical, or at least poorly considered. To be clear, I don't think anti-kids-these-days-drinking attitudes are categorically extremely hypocritical, just often so.
It's not hypocritical, regardless of whether the risks existed then. To say "I was wrong, even if I didn't know it. You should avoid being wrong as well" is in no way inconsistent or hypocritical.
I had this discussion with my mother (who went to school in the early 70s) when I entered school. Her position boiled down to it being reasonable for her to drink because it was legal, and unreasonable for me to drink simply because it was illegal. Now, I don't equate legality to morality, in no small part because she didn't raise me to do that. When pressed to actually explain her disapproval, she relented and admitted that her position was hypocritical.
Hypocrisy isn't about changing your mind. It is about holding yourself to a different standard.