I have grey hairs at the age of 18!?!?

I'm only 18 almost 19 and about a year and a half ago I discovered a grey hair, now I have about 5 (that i know of). I'm seriously freaking out about this. No one in my imidate family, mom, dad, both grandparents have gone gray prematurely. I do have horrible anxiety and I tend to obsess over things, like this, could this be the cause? Please someone give me some insight. I don't want to have to dye my hair for the rest of my life. It's not fair that I'm 18 and going grey. Please help me.