Physical exercise is more vital for older people than younger people. (Body 1)

First of all, I had two grandfathers, one for on my father's side and one for on my mother's side. However, My paternal grandfather did not really exercised and usually stayed inside home. On the other hand, although he was not quite diligent, my maternal grandfather exercised at least twice a week.
So as a result, the one who worked out even a little had lived much longer than the one who did not workout at all. even He got often got ill and he came back home occasionally got injured when he went to the park or somewhere.
I must say, those issues are not quite related to the people who are young.
Therefore, I can assume from my two grandfathers' cases that working out is more effectivebeneficial to elder older people because more people get old more they become weakened the older people get the weaker they become. 

Note.
Can I write 'to work out' instead of 'working out' ?
Does to sentences have similar meaning?

Thank you in advance.