Odds of Getting In
The odds are good of you getting into a career in sailing or fishing or working on watercraft somewhere. You may have to go out of your way if you don't live anywhere near a major body of water, but at least you do have options.
Your odds of becoming the captain of the ship? A lot tougher.
We've already discussed the Navy and the Coast Guard, where you'll have to work your way through the officer ranks for many years. The same is true in the cruise line and merchant sailing industries. You'll need a long, well-established reputation of excellence before anyone's going to hand you a ridiculously expensive boat to command.
You could always buy your own boat and captain the thing yourself. You may have no clue what you're doing and have trouble keeping a crew or passengers—but hey, even if you're the only one on board, you're still the captain.