Is it Normal to Get Gray Hair at My Age?

I'm a 13 year old boy and I have been getting gray/white hair towards the back of my scalp. My mom cuts them out so no one can notice, but they regrow. There's not a lot, maybe like 4 or 5. And I've started to get a few around my groin area. But, why am I getting them? Is this normal? Is there anything I can do to prevent this?