The rule is "Curfews: Ship's management reserves the right to enact curfews on an individual, group, or ship-wide basis, if in the sole judgment of the ship's Captain, such steps become necessary to ensure guest or crew safety."
Thus some cruises have them and some don't. In the cases where we have encountered curfews, it was clearly stated in the Cruise Compass that those affected were not allowed in public areas after the curfew time unless accompanied by parents/guardians or if they were engaged in an activity controlled by the ship's youth staff.
So, that is the rule as stated in the RCI Guest Conduct Policy. Since this forum's management does not endorse breaking the rules we'll end the discussion now, since the RCI policy has been covered.