The human body changes continuously throughout life in the first 18 years. A person evolves from a helpless  newborn needing its parents for survival to an independent adult capable of raising his or her own children. In their adulthood men and women are in their physical Prime. From the mid 30s onwards however the body slowly begins to decline .The rate of deterioration varies widely from person to person and depends on Lifestyle factors such as diet and exercise as well as genes.