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.
Most boys start puberty and begin their growth spurt between ages 13 and 15. Their growth spurt also lasts for a year or two and during this period they may gain as much as 4Â½ inches in height per year. By age 15, it is common for boys to become taller and heavier than girls. After the growth spurt, growth continues but slows down to a steadier rate. It is important to note that growth period can occur within a wide age range. Each individual may experience growth period earlier or later than the average age.