There will be many teens in that age range. Especially in July. If it were during the school year there probably wouldn't be that many but at that time of year they will not have any problem finding people there own age to hang with.
Not going on the Valor, but from past experience, I know they will have a blast.
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