Physical development can mean either the natural evolving and growing of a child into an adult, or a program that is done by an adult in attempt to get in better shape. In the case of children, there are certain marks in development that happen over a certain period of time.
Physical development in the form of stature and growth will occur for up to 20 years after a baby is born. As height as well as weight increases, a person's proportions will change as well. As a baby, most people have a relatively large head in proportion to their bodies, and this becomes less so as a baby grows. By the time they reach adulthood, most people have a relatively small head, with a long torso and long limbs.
The speed of physical development is most rapid in the months immediately after birth. After a rapid spurt for the first couple of years, growth is slow until puberty. There are are also many other factors that figure into a person's physical development. Genetics play a major role in determining just how much a person is going to grow and at what rate they grow. Another factor is environment. Without the proper food and nutrition, a person will not develop as they should and the effects will last into adulthood.
Adults who want to live a better life will often start a physical development regimen that includes dieting and exercise. Adults who want better muscle definition and strength often start weight lifting programs. Consult with a doctor before starting any kind of weight program or diet, as these programs can sometimes do more harm than good if not done correctly. Cutting down on red meat and eating more fruit and vegetables is one of the best ways to lose weight while starting an exercise program that includes stretching and walking.