I can't say how old they will be, but after 18 cruises we found that the longer the cruise the older the guests. The short 3 - 7 day cruises seem to be more of a party boat atmoshere in our opinion.
I am new to this forum. When you say CP, Do you mean the Crown Princess?
We took a 16 day Panama cruise on the Crown and on that one we were in the minority ages of under 45. Another couple we met on that cruise complained about how everyone was much older. It was a cruise where you spot the young people from across the room because they didn't blend into the crowd. We met some of the nicest older people on that cruise.
You can learn a lot from the older generation. To be honest, being on a cruise with noisy, running around kids is not my idea of cruising.
You will have a great time. Keep an open mind.
One more reply to your question.
Being up late at night and into the wee morning hours alone is not such a bad thing. We've spent many cruise sea nights observing stars or distant storms or nearby ships. It is so amazing. Down in the Southern atmoshere you can find the Southern Cross.
Early morning sunrise at sea is also a experience as well as the early mornings that the ship sails into port.
Rick, the age range on the Caribbean Princess will be about the same as it was on your last cruise on the Grand.
Princess attracts a wide age range and very diverse passengers.
If you are planning on sailing during school break there will be more than the usual amount of kids aboard