As we went through all these factors, it seems that nothing can prove that people will get exhausted when they are old. And, this is a good sign, indeed, since we will are gets old anyway.
You will say, "Hey, man. You can't say that, you don't have enough sample to cover your back." OK, I will say, don't take it seriously. We can never predict the future, all we can do is to have a positive attitude no matter what trouble we will face.
So be it, se ya! :)