Your story sounds familiar. I am just getting back into cycling, after 30 years away. I was also in the Navy (Lieutenant), not career, but I grew up in Annapolis. It was a lot quieter back then (I'm 59), and it was (and still is) a beautiful town. I live north of San Diego now, where coastal rides are level and East-West rides are hilly. You can get any mix you want.
I only started cycling again three months ago, and got a road bike -Fuji Marseille- light as a feather, easy to ride. Bikes sure have changed in those 30 years. I used to have a Bianchi, steel, Campy friction shifters, sewups, and toe clips. No helmets, no lycra, no carbon. It's not hard to get used to the new technology.
My goal is conditioning and weight loss. I couldn't make it over the hill near home when I started, and now I grind away and keep my heartrate in the 80% range. Thirty miles is still a long ride for me, though. I admire you for doing centuries. How long did it take you to get in shape for your first one?