Excercise and fitness in old age
Not all "wear and tear" is bad. I will provide only one example. Trust me, I can provide many more, but I think one is sufficient to answer your question.

Exercise (against resistance, e.g. even gravity) is known to strengthen bones, for example. The stronger your bones, the less likely they will break as a result of a fall. While that sounds kinda "meh", it's incredibly important in the elderly, because once they sustain a fracture, their activity level falls dramatically for fear of sustaining another fall/fracture. Because of this, they have a decrease in muscle mass, a decrease in lung capacity, a decrease in cardiac fitness and an overall acceleration in decline of motor function, as well as a decreased quality of life.


  Low-impact fractures, commonly called fragility fractures, have even higher mortality. Older patients with injuries from a fall have five times the mortality that their same age colleagues have from injuries from MVCs (motor vehicle accidents.) Five-year survival after an osteoporotic hip fracture is similar to that of patients with breast or other cancer. Almost one in 13 (7.5%) of those with fragility fractures will die within 90 days of fracture.* ...A fracture can be a devastating blow to an older adult’s health and independence, decreasing functional status and quality of life permanently. While some may recover their independence, half of older adults will require home health care in the 6 months following a fracture, and many will have long-term functional decline.


"Wear and tear" is good for muscles, bones, the heart, the lungs, balance, proprioception, and a number of other systems which help to prolong life, as well as the quality of life.

*Mortality is mainly with regards to hip fracture.

Fractures in Older Adults