To grow old - means to be exposed to the irreversible destructive processes occurring in an organism. The maximum frequency of warm reductions and intensity of a metabolism in the course of time only decrease.
Some kinds of sports, for example, gymnastics, very quickly and with all evidence find out this prompt decrease of our potential possibilities. Usually appreciable recession of physical possibilities of an organism begins after thirty years.
The same picture, by the way, is observed and concerning abilities of other sense, in particular in such intellectual disciplines, as mathematics. However, there some progress is not excluded up to 50 years.
Aging - progressing decrease in possibilities of the person which reminds not which process of deterioration of the car. Inevitable, inevitable ageing by the nature is result of action of the certain internal mechanism which with bad health works for people in the accelerated rate.