On average girls start to go through puberty between 10 and 11, and usually complete it by the age of 17.
Public hair is often the second noticable change in puberty, usually within a few months of your breasts starting to develope. You will start by getting just a few hairs and within 6-12 months you will have too many to count and then it wont be long before you have got dense hair all over the public triangle.
So to answer your question, yes it is perfectly normal to have public hair at the age of 13. It really depends on how quickly your body is developing. If you have not started to developed any breasts then I wouldn't expect a lot of pubic hair to grow.
I really wouldn't worry about it, you will develop eventually when your body is ready to. Everyone is different and will develop at different rates.