While most girls will get their first period around age 12, the range can run from age 8-16. Most of these girls are normal by biological standards, because puberty is a complex process of brain, body, and hormonal development. Still, there appears to be a trend toward precocious puberty in some boys and especially in girls. Precocious puberty is the clinical term for those who experience abnormally or unusually early puberty.

Every child is unique. When a child begins puberty depends on a variety of factors, including family history, ethnicity, and nutritional status.

The onset of puberty is marked by the appearance of pubic hair and breast buds in girls. Next come breast growth and body shape changes in girls and testicular growth in boys. Menstruation and voice changes come later. On average, menstruation occurs about two years after puberty begins.

Until recently, normal puberty was thought to begin between ages 8 and 14 in girls and between 9 and 12 in boys. But, recent research has found that puberty occurs as early as age six in girls of certain ethnic backgrounds.