The minimum purchasing/public drinking age is 18 (other than a single pint with a meal), but there's no practical restriction on parents letting their kids drink in private. My parents encouraged me once I was around 16 to join in with the adults whilst they had drinks. This led to me getting silly drunk a couple of times but with proper supervision. Same thing with going to some college house parties with 6th form friends - their parents knew that at the end of the night all the kids we're being picked up by their family.
The problem is if parents don't consider this and just ban drinking for kids up until they leave the house and aren't under their control any more. That's what causes people to go out of control at Uni since it might be literally their first experience with alcohol, or at least more than "1 glass with a meal" etc.
In MSU of early 00's most students drank a lot. I certainly did, mostly with other people from schools #2 and #57 already mentioned in this thread. But there was another company with a reputation of "real crazy drunkards". They were from another excellent high school, distinct from the Konstantinov lineage: the Kolmogorov's boarding school. Most of them left parents' house at age of 15.
My sister was at a private school in the UK and they were given drinks(a single glass of champagne) at certain events even before they turned 18, with permission from parents. Like you said, it's only illegal to buy alcohol under 18, but there's no problem with consumption itself.
I was given Buck's Fizz (Champagne and orange juice) when I was 5, at the birthday party of a super-posh boy who lived in the village. His grandfather didn't even ask my mum first. Upper class people apparently have different rules.
At Imperial, when the Google London office was new, the feedback from staff for why so few students hung around at their recruitment event was the lack of alcohol. Overturning this HQ-imposed very American policy apparently took significant effort.
The minimum purchasing/public drinking age is 18 (other than a single pint with a meal), but there's no practical restriction on parents letting their kids drink in private. My parents encouraged me once I was around 16 to join in with the adults whilst they had drinks. This led to me getting silly drunk a couple of times but with proper supervision. Same thing with going to some college house parties with 6th form friends - their parents knew that at the end of the night all the kids we're being picked up by their family.
The problem is if parents don't consider this and just ban drinking for kids up until they leave the house and aren't under their control any more. That's what causes people to go out of control at Uni since it might be literally their first experience with alcohol, or at least more than "1 glass with a meal" etc.