Age, and usually couples are with couples, singles with singles. My husband and I got married at age 22 (a little younger than average), so every time we cruise we're put at the honeymooners table (and sometimes we're still the youngest!) - but we don't mind, it's nice getting the cake even when you've been married 3 years!
I have been on three cruises (i am 22) and have been seated with multiple ages and types. I have been seated with singles, parents, couples, older couples and families??? Not really sure why?? Some how ended up at the exact table on two different cruises ( 1 on the fantasy 1 on the fascination -sister ships) weird? but I havent seen a real pattern.
I am a travel agent/cruise specialist and Carnival does its best to match you with people in your age group to make sure everyone is as compatible is possible. You might ask for a smaller table, ask your travel agent to request a slightly different age group. It also depends on your seating, early vs. late. Those who like the nightlife tend to enjoy the later seating, while early-risers, families etc. like the earlier seating.
If you don't feel comfortable with your seating, you can certainly speak with the maitre d' when you first arrive on the ship. They have the seating arrangements in a public location on the ship (check the daily newsletter for the times and location) and the dining staff is usually able to accommodate any changes. Also, if you get to your table and are not happy with your tablemates, you can speak to the maitre d' in the dining room and request to be moved. The maitre d' and host staff are usually very discreet with these changes and you just end up disappearing mysteriously instead of causing uncomfortable situations with your tablemates.
Sometimes.... we ended up at a table for 10 on RCL's Alaska Cruise... My wife and I and a family of 8 Chineese people, with only 1 that even spoke rudimentary english. While we love to meet new poeple, after two nights finally realized that we were not communicating, and asked to be moved to a table with some people we had met.
All went well for three days, until the Romanian waitress from the previous table came over to our new table and made a big scene asking what she did wrong, and why we moved, and that she lost five days of tips... what a mess.... loud and vocal... My crusiemates, on their 7th cruise, went and got the Matri d' get her off our backs....
RCL Legend of the Seas July 1999 Alaska
NCL Majesty Feb 2003 W Carr.