Lycée would be the equivalent of high-school, with a typical age of 15-18 (https://en.wikipedia.org/wiki/Secondary_education_in_France).

Why would it not be tolerated? They are almost grown up. If they are considered mature enough to make their driver's license, why wouldn't they be allowed to drink?

They're also old enough to have sex, but they probably aren't supposed to do that at school.

> 17 year olds drinking beer between their late afternoon classes is not unheard of and often tolerated.

Well, it's between classes, in their free time.

Not clear if they're doing it at school or outside of school. If the latter, the analogy doesn't apply.

> If they are considered mature enough to make their driver's license, why wouldn't they be allowed to drink?

Don't know, seems natural to me, since I've grown up with that mindset but not all nations agree on that.