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.
Some girls get their first menstrual periods late in this stage. 4 Age Range: Usually 10-16. Average: 13-14 Pubic hair growth takes on the triangular shape of adulthood, but doesn't quite cover the entire area. Underarm hair is likely to appear in this stage, as is menarche.