Mischief,
5 or 20 years old, it's not too early to make plans. Scubatooth seems to have made some good plans, including topside training in photography and production.
I just submitted photos for my first paid photo assignment, which was my dream since high school in the early 80s. The pay for this first assignment was a few thousand dollars, which is on the high end for freelance photographers. My second gig will pay me nothing, but I get to keep the snorkels I photograph for an equipment review for a dive magazine (which normally pays $50 per published photo). That shows you the extremes for pay in photo assignments. I can't speak about in-house photography jobs b/c that's not my experience, but my main advice is to have a backup source of income if you're going the freelance route. I know many artists/photographers, and making ends meet and getting assignments in the beginning can be frustrating. I still have my day job, and it's really difficult to give it up for photography full-time because the day job pays quite well. In fact, without the day job I don't think I could have afforded the outlay for quality camera equipment, scuba equipment, and frequent trips to other dive destinations.
Try topside photography first. Take some classes, read books, and practice practice practice. A digital camera will help b/c you can learn without dishing out tons of money for your mistakes. Ask your friends, family and maybe people on a photography forum to comment on your photos. The responses you get should give you some idea of how your photos stack up. Look at professional photographers' work in dive and other mags and see how your photos compare -- that's a good way to figure out whether you have the potential for a successful career in photography.
If you've determined that you have a good grasp of photography, your other emphasis should be on diving. You'll see lots of threads here about being a good diver first and a photographer second. No bumping coral, no harassing sealife, no unsafe diving practices. The DM training you mentioned will help loads in that regard.
Good luck!