Reasonable diet, reasonable exercise and healthy habits.
It is very important for any healthy, sub-healthy or even physically damaged body.
The most important thing is mentality. If you lose confidence in your body, your body will get worse. On the contrary, keep an optimistic attitude and believe that you are fine and your health will get better and better.
Maybe you think what I said is false, but it's true.
The best' treatment' for the elderly is to let him live happily and guide him to live healthily and happily.