A moving door hinge never corrodes.
Flowing water never grows stagnant.
Even in the autumn of your life, you cannot give up growth. If you do, you only invite decline.
All the different aspects of a person — body, mind, and spirit — have one curious quality : If they cease to be exercised, they stop growing. Once they stop growing, they begin to atrophy. That is why, no matter how much you have accomplished and no matter how old you are, you must keep exercising all parts of yourself.
We only grow when we are challenged. Muscles do not strengthen without resistance. Mental faculties do not sharpen without critical thinking. The spirit does not soar without something to excite it. It may seem like a great effort to constantly try new things, but unless you do, you fall out of your heights very quickly. The constancy of physical exercise, varied from time to time into new routines, and the constancy of mental and spiritual challenges are essential to stave off the infirmities of aging.
We cannot reverse aging completely, but we can slow it down. As long as we are vital, we will not suffer as much. Although aging is natural, sometimes following Tao means more than following the route of least resistance. Why slide into old age, illness, and senility? The way of challenging oneself is also a valid but difficult path. Sometimes Tao chooses the difficult over the easy.