I was in the UK last summer with my two teen-aged nieces (London and Edinburgh). I ended up getting two rooms at both hotels. Three "adults" (17, 18, and me) was too complicated, plus their room was a pigsty! So glad I had my nice clean bath and bedroom to myself I'm not sure anyone would have required ID for the 17-year old (and she was only 16 when I made the reservation - just turned 17 before we went on the trip) if I went with a family room; however, I didn't want to deal with the hassle. It meant staying at less expensive Marriott properties, but worth it in the end.