Depends on the ship, I think. Navigator should still be going with the 9-11 age group for Adventure Ocean, which means your 12yo would be in the teen club. Security in the teen club is, as you might imagine, more relaxed than that in the kids clubs. I would take your 12yo to the social on the first night, to gauge how many younger kids are there. If the group trends more towards the upper limit, they may not want to go, which is what my 12yo daughter opted to do (or I suppose, not do) on our Indy cruise.