I was introduced to diving in the late 70's when I was in college in Florida. I never got certified but have always been happiest either in or on the water Now I can add under the water to that.
I woke up one morning earlier this year at 49, with a wife, 3 teenagers, two cars, a mortgage, and all thr other trappings of modern life. I decided it was time start living my life for me as well as others and do something just to make me happy. I got certified. I took my classes at a local dive shop in June and my certification dives in the Keys in July. I continued on and got my advanced card, and did Nitrox in October. I have 28 logged dives so far.
I am now 50 and overweight; morbidly so at 5' 10" and 380 lbs, but I've lost 40 lbs this year and diving has been an additional outlet and incentive to continue to fight this battle.
I do laps so I didn't have trouble with the 200 meter swim, I did it all freestyle but if endurance is a problem you can slow down and change strokes. Try the side stroke to rest, as long as you keep moving forward.
I plan on getting my rescue diver cert next year, and who knows from there. I'm waiting for a wet suit to be delivered tomorrow that, if it fits, will enable me to continue diving this winter.
We live in the same area. There are a few good diving sites within a 2 hour drive of here. maybe we can buddy up sometime.