you just answered your own question. puberty at 9, puberty doesn;'t also last years in terms of getting pregnant.
The changes take place in all boys and girls but they will start at different times and take place at different rates. Not everyone starts puberty between the ages of 10 and 14, some people start younger, and some much later. Similarly, in some people all the changes take place in two years, and in others they can take as long as four years. Generally they start between ages 7 and 13 in girls and ages 9 and 15 in boys