"If you begin a daily walking program at age 45, he said, you could delay immobility to 90 and beyond. If you become a couch potato at 45 and remain so, immobility can encroach as early as 60."Link: http://www.nytimes.com/2010/10/26/health/26brody.html
"The good news is that the age of immobility can be modified. As life expectancy rises and more people live to celebrate their 100th birthday, postponing the time when physical independence can no longer be maintained is a goal worth striving for."