We cruised on the Millenium, which is the sister ship with a 10 year old boy and 15 year old girl and they loved it so much we are cuising with Celebrity again this year. The 10 year old boy we never saw, always at kids club!! Which was excellent, well trained and flexible. My daughter didn't fancy teen club so although with us had a ball dressing up, sunbathing and met other teenagers who she met up with in the evening.
To be honest the Constellation is a much more sophisticated experience than P&0 but it is more adult oriented and whilst there are pools, an arcade room and such as table tennis etc there are not as much teenage oriented things as on RCI or P&0.