On MSC ships there is no curfew and teenager are allowed in the disco all night, this means a lot of fun for them, but also little sleep, expecially on port intensive cruises.
On our last cruise, we let our 14yo stay up really late every night, even when she had to get up early for excursions on the next day, so she actually slept 6 hours or less every night, except for sea days, when she could sleep in.
She was really tired of course, so we convinced her to take naps in the afternoon on most port days. Actually, she always had better plans for the afternoon, but we insisted a bit and she surrendered because she knew she was exhausted.
Do your teens sleep enough on cruise? Do you enforce early bed times when they have to get up early? Do they ever take naps in the afternoon or before dinner? Do you let them sleep in?