Info off Celebritys Website:
What is Celebrity's policy regarding unaccompanied minors?
No guest under the age of 21 will be booked in a stateroom unless accompanied by an adult 25 years or older. This age limit will be waived for minor children sailing with their parents or guardians in adjacent staterooms.
Individual staterooms can be booked by married couples whose minimum age is 18.
This is off Celebritys website. So you should be fine. We recently cruised Celebrity, and there wasnt alot of younger people. I am not sure if you will enjoy them as much, they tend to draw a older crowd. We are in our late 20s, early 30s and was bored alot.
We usually like Carnival. But thats just my opinion