How can i get my hair to grow?

Im 15 years old and when i used to live with my gma when i was a lil kid she ALWAYS cut me bald "skin Bald" cause she never learned how to cut hair. :( now that im older and i can learn how to do things for my self i always admire braids. well for some reason my hair wont grow long enough ( at the most half a inch. My mom says its because of my father who's hair didn't really grow that much. Is there any way i can get my hair to grow anymore (i don't really believe her) please help me