Hi Conundrum1 and welcome to Cruise Chat.
In addition to Cruise Fanatic's great suggestions, I would add that you should not cruise during school holidays or Spring Break. I think the earlier in February you cruise, the more likely you are that none of the high schools or colleges around the country are on break.
You may also want to look into Holland America, which will make you feel young as they tend to attract more seniors than people turning 50.
Also, the longer the cruise and the more expensive the cruise line, the fewer children will be onboard. I don't know if this fits into your plan.