Many girls want to know when their breasts will develop or when they'll get their first period. If a friend or a younger brother or sister develops first, they may worry that there's something wrong with them. Physical development starts at different times and progresses at different rates in other people. So, the beginning of the development that comes with puberty varies from person to person — and that's completely normal.
The earliest physical puberty change for girls is usually breast development, which most often begins around 10 or 11 years. But it's perfectly normal for breast development to start anytime between the ages of 7 and 13. If your breasts have not developed at all by the time you turn 13 and are worried, you can see a clinic for an examination.