No milk is produced during pregnancy, but milk ducts and alveoli proliferate during that time, and the breasts enlarge. Once the baby is delivered, the pituitary secretes prolactin, and milk is produced. Suckling of the baby at the breast enhances milk production. Development is a lifelong process into adulthood. After that period, aging occurs.
Gerontology is the study of aging.
One theory of aging suggests that aging has a genetic basis. Cells can divide only so many times. As we grow older, it may be that more cells age and die. Also, some cell lines may die before that maximum number of cell divisions has been reached. Some people may have genes that code for efficient enzymes that remove free radicals, causing the individuals to live longer.