I'm 12.. and I have many many grey hair. My hair colour is black. My mother said it has something to do with genes. Because my father... and his mother had grey hair since they were in their 20s. But in my case, I started at age 8 or 9. My father won't let me colour it so.. is there another way I can get rid of them besides colouring?

The only way is to color your hair.

Honestly though, your parents are right. You are too young to color your hair. When you're a little older, then perhaps yes. That is after you ask them.