I don't know how closely they watch this. The age limits are more to monitor size and weights for some of the tours. You can speak with the excursion desk when you get on the ship and see if they can ask the tour operator if it is ok for the 11 1/2 year old. Or you can go online and try to book your our tour. Most of the tours booked outside of the ship will take younger childern as sometimes the age requirements are put in place by the cruise lines to help with liability issues. This may be your safer bet since if you wait until you are on the cruise, the tour may be sold out.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007