I know there have already been discussions if Butterbeer and other drinks in HP are spiritous or not. I'm NOT trying to re-hash that discussion.
But I am going to assume that at least the wine & "oak-matured" mead mentioned in the books can have intoxicating effects like the real world. I'm not sure about the UK, but the minimum drinking age in the US is 21 years. I seem to remember references throughout the novels (although I can't remember exactly where) that say something to the effect "just get them to drink a few butterbeers/mead/wine/etc and they'll start talking" (they weren't talking about potions/magic either).
I can remember at least one concrete example that I can use for this question. Towards the end of Chapter 18 of HBP, Professor Slughorn gives Harry & Ron some mead on Ron's 17th birthday as a pick-me-up for Ron after he gave Ron an antidote to the love-potion-infused chocolates that he accidentally ate.
Assuming there is a minimum drinking age higher than 17 in JKR's home county, why would she include this kind of under-aged drinking in a children's novel? Is the thinking that the kids can do magic and make potions which can be much more potent than spiritous drinks so it doesn't matter? Or is there compelling evidence that wine & mead are non-intoxicating in the Potterverse?