ANDY'S ANSWER: If you haven't started puberty yet, there's no way to tell when you will get your period. Your Mom may have some inside information if she was a late bloomer herself. Even if she was however, it doesn't guarantee that you will be the same.
You will have some signs that puberty has begun and you can somewhat gauge when you can expect your first period from these signs.
One of the first signs that you have started puberty is that your breasts will have started to bud. Once that happens, your period should be along in about 2 years later, so pay attention and mark it down when it happens.
Another sign is public hair. When your breasts have started to develop and you have a grown a triangle of pubic hair, your period is probably only months away. About 6 months before your first period, you may also notice a small discharge from your vagina.
Whether you are an early starter, a late starter, or somewhere in between, it has nothing at all to do with your life as an adult and in the end is completely irrelevant. Your body will know when it's ready and will proceed when it is. It's kind of like when you got your first tooth or started walking when you were a baby. It just doesn't matter now.