Cellular clock theory is related to aging. In this theory, the cells of the body are limited for some time and can repair for a limited period. As the person gets older, the collagen that is responsible for rejuvenating gets deteriorates. It creates the skin look saggy and wrinkled. This theory tells about the aging process in human beings. There are several types of aging theory and this is one of them.
Thus according to the biological theory, it is also called a cellular theory of aging theory. At this time our cells are limited for divide.