Two DD, 16 and 18, I allow DD16 alcohol (usually a small wine or half a cider) when we go out for meals. I believe this is legal, she drinks sensibly at parties anyway.
My dd went out with sis's dd 18 and 19 for a meal at a chain pizza place. They ordered a bottle of wine to be shared amongst them, all were ID'd which I'm sure is standard but they refused to allow DD 16 to share the wine and she ended up with a coke.
She wasn't that fussed, it was on Friday and has only just come up in conversation. I think she should have been served, she was having a meal with 3 legal adults. Should she have been? Maybe the adults need to have parental responsibility?