I guess I qualify as one of those.." Older" sailors.
So, I'll give it a try. My 1st thought, is to suggest that you continue your studies and keep working toward getting at least a bachelors degree. I anticipate that some folks may tell you that you can make just as good a living learning a trade. Rather than debate that, I'll simply suggest that a college degree will never hurt you. And that you can have both..a degree and a trade. While going to school you could work at a marina or in the boating industry and begin your networking in that world. Establishing your work ethic and reliability, building relationships and networking as much as you can will pay dividends..down the road.
There are lots of ways to get into the boating industry..but since you said that you want to be on the " deck" Have You considered the Coast Guard..the Naval..or the Merchant Marine Academies...? Very competitive but something worth considering.
You can also enlist and learn a skill/trade that way, getting paid as you go.
If you want to be in the marine industry: Schools: Maritime Schools
If the services are not your cup of tea, I'd start finding a way to get on boats learning and gaining sea time and start working toward licensure.
As far as other trades...there are almost too many to mention. Diesel mechanics, electrical, sailmakers, welding, diving, etc etc.
Noaa often posts civilian jobs on ships for qualified individuals as does the park services etc etc.
Life has a way of unfolding..despite our best plans. I think the best advice I can give you is to obtain the best education you can in the field you choose, network, build a solid professional reputation, build and maintain relationships...and opportunities will present themselves...
Best of luck, in whatever you decide..