Yes - you probably are a bit to mainstream for cruise lines. I'd ballpark the average cruiser's age in the 40's, maybe more. The DJ gig is closer to a wedding crowd. The 'younger' groups you'll see are those that you'd see at a theme park - young families with kids. Carnival's probably the closest you'll get to "urban", and that's pushing it.
Be aware that "DJ" at night is just a small part of the job. Whatever cruise line - it's a part of the cruise directors division, and you'll be doing other duties - like gangway, meet n greet's, socializing, trivia's - On Royal Caribbean, you'll be belaying on the rockwall . . . If you think hotel on the seas - that's the crowd.
That being said - just google "employment" or "careers" and the cruise line, and you should be able to find the employment sites. (ps - and add "hiring partner")
If you're looking for a more of a party atmosphere - you might look at Caribbean land resorts like Club Med.
Seven Seas Group : Home : Recruitment for jobs on cruise ships.
is a US recruiter and if you're not US - they might be able to point you to whoever works in your country.