Is gray hair caused entirely by hereditary genes?

I am 17 years old and I am going gray! lol. my mom started going gray in her 30s but not in her teens. i know that gray hair does run in my family but nothing like what i have- most of my relatives have gone gray in their late 30s and beyond! I have a relatively large patch of gray hairs and i notice more and more grays in other areas of my hair also. what could be causing me to go gray so young and is there any way to prevent further grayness? i know i can dye my hair and i already do that but are there any other solutions because i really don't want to be dying my hair for the rest of my life to cover gray hair when i am only a teenager!!!!! help!