You might check into one of the shorter cruises (3, 4 or 5 nights) on Carnival or Royal Caribbean. Those two lines are very popular, and the shorter cruises often have younger folks onboard. You should know that there may be a requirement that at least one passenger per cabin be 25 years old or more. Be aware that passports will be necessary as of Dec. 31st this year for any U.S. citizens returning to the U.S. from the Caribbean - this is a new ruling.
Thank you for your service to our country! I wish you good health and a safe return home!