There's nothing wrong with you at all. People are all different, and you will start soon enough. Some girls start at 10. Others at 18. It's down to your body and can be hereditary, or affected by diet, body size, etc etc etc
Also - don't be shy about speaking to your gp or school nurse. You might be mortified, but they've heard it a thousand times. If you're worried they will be able to help you, honestly.
When I was 12 all I wanted to do was 'start my period' and then when I did at 13 I was so chuffed. However the feeling didn't last after I had experienced it a couple of times lol so cherish every moment that you don't have them.
As Whickerman has said, some people don't start until they are 18, I think they are the lucky ones!!
sweetheart dont be in no rush as when they do start you will have them for many years and they can get on your nerves like when you are going somewhere special or on holiday and your period starts you will have the worry of wether you may leak and wont want to wear white just in case, and unless you are goig to use tampons its not the niciest of things with a towel in your pants
It really can start at anytime and so when your body is ready it will happen. It should be anytime soon and so make sure you are prepared with towels in your bag