The average age to start your period is 12, but many girls start younger, and others start later.
It might take up to two years for your period to get regular because the hormone surges are uneven. At first, it's common to have one period, and then not another for a few months. But even if you don't have a period every month, you can still get pregnant.
Many girls start their periods around the same age as their mothers did. So ask your mother when she started her period, and how it felt. If you haven't started your period by age 16, you should talk to your doctor.