Everyone goes through puberty at a different time, which means girls get their periods at different times too. Most girls get their period about 2 to 2.5 years after they notice their breasts starting to grow. This means they usually get their first period between 11 and 14 years old. There are a lot of things that affect when you get your period, including your genes (which affect what hair color you have, how tall you are, and even when you get your period), hormone levels or chemicals in your body that tell it when to start having your period, what you eat and drink, and anything else going on with your body or health. If you are worried or more than 3 years have passed since you started breast development, you should talk to your parent (or guardian) and your health care provider. Make sure to let them know any questions you have.