Weight loss and perseverance

Lean muscle, burns more calories at rest. The more lean muscle you have, the more energy your body uses just sitting there. Like having a HEMI idle versus a /6. it uses more fuel. Now, add moderate activity, ie. step on the throttle and use even more fuel.... You're going to see even more progress. Lean doesn't mean HUGE. You don't need to be a beast.

In a nut-shell, yes.
In your case, you had one of the best type of physical activities, outside smart weight training, Motorcross BMX racing. Vigorous full body activity. And thank you for your service BTW !
Unfortunately, as most of us do (I took a turn myself), life changes and we abandon good physical behavior. Some will excuse it as a right to getting old. And then wonder how they got to where they are bodily.
There are some very important dynamics, particularly in the male body, that is never realized outside the bodybuilding world. As the presence of body fat goes up, so does the production of Estrogen. It takes place in the fat cells. In fact, if a man decides to go on TRT in his later years, if the Test is injected into fatty tissue, there will be NO Testosterone boosting effect in the body! (I don't do TRT myself for other reasons)
Estrogen will actually REDUCE the production of Testosterone. Estrogen is also Catibolic. Testosterone, aside from stimulating muscle growth (Anabolic) in male AND females in its natural state, also aides the body in staying lean. And when you combine this with proper exercise, it's a win, win.
Look up Leptin, and see where that takes you. Discounting hormone levels in the body is pure FOOLISHNESS.
The answer lies, as with anything else, starts with awareness followed with good info. Then vet that info to the ninth degree. There's a lot of bad info out there. Like the assertion Testosterone therapy causes Prostrate cancer. This is the turd that never flushes! The study that concluded this asinine claim in a study conducted in 1952 on a man who was unfortunately castrated by an unfortunate accident. It did give him prostrate cancer.
The conclusion here is simple, if you don't have your balls, don't go on TRT. If you have your buddies, and feel you need the boost (most of the time its medically) then go on TRT! Your prostrate will be FINE.
I'm only scratching the surface here...
Diabetes could be stopped tomorrow, if people would do their research. I'll stop now..