I still haven't started my period and well I just turned 13 and all of my friends have should I be worried
Don't worry, every girls body is different and develop at a different speed. You will get your period when your body is ready.
Lol dont worry, you should probably be preparing because i got my first period 2 weeks ago, and its really a big surprise, you just wake up to blood all in your panties. It isnt pleasent. But just to be safe, start preparing!
Also, i had really bad cramps and diarrhea a few days before i got it.