Undefined, I will try to make this as brief as I can, because there is so much that I could write, but feel free to ask me to expand on any of the points if you'd like to know more. I'm going to ignore your husband's mobility issues for now, in order to list the things I would recommend, in order of preference and beneficial effect. So I would say to look at:
- Weight Training
- Clean diet and quality foods
- Certain super foods
- Supplements
- Avoidance of chemicals
WRT weight training, it really is the single most beneficial thing you can do to increase test levels. It has the added benefit of literally shredding fat and building muscle, so it has a very positive mental / self image effect as well. And depending on how you train, it can also be a very effective way of cardio training. Obviously I don't know what his mobility issues are, but is there any possibility that he could work around them? At 42, my hips are too tight for me to do some of the exercises I would like to do, but I can always find ways around them. And actually, my enjoyment of the training means that I try to find ways to fix my mobility issues rather than simply accepting them, so if there is any way he could get back in the gym and enjoy it as he obviously did before, that would be brilliant for him.
I don't know what your diet is like, so forgive me if it sounds like I'm making assumptions. But the cleaner and better quality the food he can get, the better it will be for his test levels. That means organic where possible, grass fed for meat. Our groceries bill is quite huge, but there are ways to reduce it if you have the time to put some effort into it. But whatever you do, really try to minimise the junk food or processed foods if you eat them. As a nutritionalist friend said to me, "If you can't pronounce the ingredients, they are not good for you". It's a simple rule of thumb to stick to.
There are also some "super foods" that apparently help - eg avocado and good quality salmon. Honestly, I don't know how many of these really have a direct effect on test levels - I tend to work on the basis of eating very high quality proteins and fats, and getting plenty of omega 3's. I'm also in favour of seriously reducing carbohydrate intake, or at least, minimising sugar, and maximising low GI carbs, eg sweet potato. These help keep energy levels high and consistent for a few hours, as opposed to the peaks and troughs that high GI carbs or sugar cause. This alone will help to control insulin levels, which means the body's hormonal balance is easier to keep in check.
I'm reticent to mention supplements, as there are many out there that are pure snake oil. That said, I can't ignore the fact that some of them do work, and even if it's a placebo effect, if it makes a difference, why the hell not? The two that I "feel" improving my test levels are ZMA and Tribulus Terrestris. They are both inexpensive, freely available, and ZMA may well help fix zinc and magnesium deficiencies which you didn't know existed. It helps with sleep as well. Tribulus has a noticeable effect on my libido, and because of that, I generally "feel" that I have higher test levels as a result. I am not claiming scientific proof of this, only listing what I see as really having an effect. Other supplements that people claim to get results from are D-Aspartic Acid and Tongkat-Ali. Both can be bought relatively cheaply. Personally they both make me nauseous and I don't feel any benefit from them, others do. It's up to you, and may be a case of experimenting to see if / what works for him. Whatever you do, avoid the type of "advanced" secret formulas you see advertised for bodybuilders. The only thing they are advanced at is parting you from your money.
Finally, and this is really pushing the envelope a little, you might want to look at removing as many chemicals as possible from his daily life. I use paraben free shampoo and flouride free toothpase, although this for me is more about being as free of chemicals as I can, not just test related.
Oh, and obviously cigarettes and alcohol, although I think the latter is good in small doses.
I just looked up and saw that my brief post is massive. Sorry about that, I really hope some of it is useful. As I say, feel free to let me know if you would like some more info on any of it.