Puberty is a time when your body goes through lots of changes. It can be wonderful and exciting, but it can sometimes feel overwhelming. This is the time when your body changes from being a girl into being a woman, and develops the ability to have a baby. All of the changes come from your body’s natural chemicals, called hormones. Puberty for girls usually starts between the ages of 8 and 13 and lasts a few years. Girls who are overweight may start puberty a little earlier, and girls who are athletic or underweight may start later.