I can also speak to some of this, as well. Two years ago I had diverticulitis(requiring a colostomy) and a mild heart attack a month later. I can say without a doubt my general physical condition at the time was awful. I don't smoke and I've never been a heavy drinker, but I was on lots of pain meds after retiring from the Navy, which I'm sure is what caused the intestinal problems. Word of warning: pain medications are a common cause of constipation, and I was on just about everything for chronic back pain. I wasn't hooked on pain meds, but the years of using ever stronger stuff to deal with it just wreaked hell on my system.
The back pain, migraines, a bad, salty diet(and attendent high blood pressure) and lots of other things made Homer something, something, something. When I had the heart attack my main artery supplying blood to my heart was completely blocked and I had to have a stent put in. I'm 54 now, and in general, I'm much better. The heart is fine and I had my colon put back together about a year ago and I am completely mobile again.
The hardest part is getting back into a physical routine again, and I try to walk every day. I live a block from the ocean so I have no excuse. I need to do more though, since I really don't need to weigh 200 lbs. Ideally, I'd like to find a pool where I can do laps, since I can't run anymore. Running used to be my favorite thing. The food is actually the easy part of getting better, I find. I realized when I stopped looking for a salt substitute, and just ate the food without it, I enjoyed it more. I eat lots of chicken and fish, very little beef and try to drink a lot more water. I still have a bad caffeine habit, but I'm slowly trying to cut down there.
Living alone probably doesn't help here, either, since you tend not to make an effort when there's no one else around. I can't speak to 'low T' but if I was tested, I probably wouldn't have very many. My point is, though life isn't perfect, I still feel optimistic. I know 90% of the challenges are in my head and I am slowly making a difference. The future doesn't look that great, but I do feel as though I can rise above it and that's the point. I came from a real low point two years ago and through determination and hard work I was able to make myself a lot better. I can do better still physically. Someone once told me that even if she got nothing else accomplished during the day, having worked out that morning was still an accomplishment that made her feel better at the end of the day. So, even if all you do is get out in the fresh air and take a walk, that's something that will help, too. I'll check out those links that Lena posted and see what else I can pick up. Life's not great, but it's not horrible, either. We humans are a resilient lot.