Yes, 'some' pubs say 'over-21s only' - this is purely at the landlord's discretion and tends to be busy, clubby city centre pubs with bouncers on the door, designed for hard partying.

As an aside, it's really a right-of-passage to drink underage in pubs. I defy anyone to find a Brit that didn't have their first alcoholic drink in a pub with their mates - not parents - under the age of 18 (and chucked out of a few pubs because of it).

I think I was about 15.

My husband was drinking in pubs in Aberdeen when he was 15.

You and your sons will be fine. Have fun!