It is only the European itineraries. I think it has to completely be outside US waters (and territories) for the policy to take place. When we did the Northern Europe Sailing in 2019 we had two members of our travel party that were just about a month shy of 21. The parents of each had to sign a waiver and everyone got special stickers placed on their KTTW cards to designate that it was ok. I think the rule was that the minor with the sticker had to be with another over 21 person (with the corresponding sticker) so that they could order drinks. They were not allowed to drink on their own. To drink with a parent on the Bahama sailings, it would have to be done on land.