Puberty and periods

Some short but important notes about girls' menstruation:

Menstruation (a period) is a major stage of puberty in girls, signalling that a girl is turning into a woman. When girls begin to go through puberty (usually starting between the ages of 8 and 13), their bodies and minds change in many ways. The hormones in their bodies stimulate new physical development, such as growth and breast development. About 2 to 2½ years after a girl's breasts begin to develop, she usually gets her first menstrual period.

About 6 months or so before getting her first period, a girl might notice an increased amount of clear vaginal discharge. This discharge is common. There's no need for a girl to worry about discharge unless it has a strong odour or causes itchiness.

Some girls may start menstruating as early as age 10, but others may not get their first period until they are 15 years old. Irregular periods are common in girls who are just beginning to menstruate. It may take the body a while to sort out all the changes going on, usually, after a year or two, the menstrual cycle will become more regular. Some women continue to have irregular periods into adulthood, though.

Some girls may notice physical or emotional changes around the time of their periods. Once girls start to menstruate, for the next two years, they usually grow about 1 to 2 more inches, reaching their final adult height by about age 14 or 15 years (younger or older depending on when puberty began). There are usually not large growth spurts once the period starts.


Sources:
http://kidshealth.org/parent/growth/growth/growth_13_to_18.html
http://kidshealth.org/teen/sexual_health/girls/menstruation.html#