Just as on the demand side, the position of the supply can shift, say from a change in the price of a productive input or a technical improvement. The Law of Supply states that, in general, a rise in price leads to an expansion in supply and a fall in price leads to a contraction in supply.
Puberty takes place over a number of years, and the age at which it starts and ends varies widely. It generally begins somewhere between the ages of 7 and 13 for girls, and somewhere between the ages of 9 and 15 for guys, although it can be earlier or later for some people.
Girls may enter puberty at seven, but will experience a majority of their growth in height when they are around 10.5 years old. Boys may begin puberty at the age of eight, but experience growth when they are around 13 years old. Since girls enter puberty before boys, they also experience growth spurts early. This can result in girls towering over boys of the same age. On an average, boys grow the fastest between the ages of 14 and 15.