The good news is that even people who have been sedentary for decades can derive significant health improvements by beginning (under supervision) a proper exercise regimen that includes strength training. Simon Melov at the Buck Institute for Age Research looked at this several years ago in conjunction with colleagues in academia - it's worth looking at his studies and the results obtained, which were astonishingly positive. In addition, as exercise changes gene expression profiles, a person's immune system also improves, thus further enhancing their quality of life.