Who knows? It is perfectly normal to have your first period anywhere between the ages of 9 and 16, but 12 is probably the most average age to start. If you are past 16 and still waiting, your doctor will probably put you on hormones, which will sort of kick start your system.
There really isn't any way to tell you are about to start. The truth is that is different for every girl. You might have heard that you can tell by how the size of your breasts. While it is common for girls to start their periods a year or two after their breasts first start to grow, it is not true for everyone.
We don't know for sure how your body decides that it is time to start menstruating. People who research this kind of thing have two basic ideas, both are about your body's size.
One is that you will start your period when your skeleton reaches its mature form, when your bones are about as big as they are going to get. As you know, you grow very fast, faster than boys do, from about 11 on. When this growth spurt is over, your period starts. P.T. Ellison, the person who came up with this idea, thinks this is your body's way of making sure that you can't have a baby before you pelvic (hip) bones are big enough for a baby to pass through.
Dr. Rose E. Frisch came up with the second theory, and this one is most popular. It is about your body weight rather than your bone size. She believes that your body has to get to a certain weight, and that 1/4 of that weight has to be made up of fat, before menstruation begins. A woman's body has more fat than a girl's body, or a man's body. Fat is the body's way of storing up calories for hard times., and it is important for women to have a little extra fat for child bearing, because carrying a baby takes a lot energy. When you have enough fat to support yourself through a pregnancy, your body gives the go ahead to start your period.
We know for sure that women who lose a lot of their body fat though athletic training, especially if they started the training when they were young, may start late, or menstruate infrequently. Also, women who lose most of their body fat through starvation, like women with anorexia, stop menstruating. Girls who are under- nourished as they grow up also start their periods later on average than girls who are well fed. Girls in the US are getting their periods earlier and earlier, and they also have more body fat than girls of previous generations. This all shows that there is some connection between your weight, your body fat and your period.
It would probably be easier if everyone started their periods at the same time, then no one would have to worry about being different or left out. But it just doesn't work that way. The girl who starts before her friends do may be envied by the other girls, but she might feel embarrassed to be different. She may even keep it a secret. The girl who starts later than her friends might feel hopelessly immature and wonder what's wrong with her. When you start your period has nothing to do with the kind of person you are, or the things you do. Your body is following its own clock, and you and your friends should respect that you are each going to be a little different. Be patient, and remember that your period is as unique to you as your eyes. Identical twins don't even start at the same time!
Some girls are very happy when their period starts. Others wish they could just make it stop. But it is probably most common to have mixed feelings on that day. For instance, if you have been waiting for it, you could be excited that it is finally here and you want to tell all of your friends. You might feel proud, and more grown up. On the other hand, you are a little embarrassed too, but you don't know why. You tell your mom, but you don't want her to blab about it to the entire neighborhood. It makes you feel funny to think of other people, especially boys, knowing that you've started. You ask your mom not to make a big deal about it, but you feel a bit disappointed, like its the day after Christmas.
Almost every woman remembers when she started her period, and each woman's experience is a little different.
In the United States, there is no official celebration, like a birthday party, for your first period. It is strange that something that is so very expected is not celebrated when it finally comes.?
Other cultures have big celebrations for a girls first period, and in some cultures a girl takes on all of the responsibilities of a woman when her period starts. In our culture though, you are in limbo after your period starts, because adults may say "congratulations, you are woman today" but they don't treat you like one. Its not like you move into your own apartment when you start your period. You look in the mirror and you look the same, but you know are not the same as you were before.
The funny thing about being a teenager and a young adult is that each year you think you are very mature. You don't act like a kid anymore, people think you are older than you are. You wear adult clothes and make-up, you shave your legs and learn to drive a car.
You can't imagine being any more mature than you are at that
time. Until the next year, or two, or three years down the line, when you
look at some old pictures and say "I look so young there! What was
I wearing?" or you think about mistakes you made then that you would
never make now. Each year you fool yourself into thinking you are all grown
up, when the maybe the truth is that you never really grow up. Each year
you learn more about the world and about yourself. So being a woman isn't
something that comes to you with your period, or the first time you have
sex, or at the age of 21, but it is something you earn through caring,
hurting and learning. It is something you will recognize in yourself one
day.