Gray hair in early 20s?

I can remember when my mom was about 29 or 30 she started buying hair dye because she was going gray. Well, I always thought it would skip a generation because she has very thin straight hair and I have my grandma's hair, which is thick and wavy. So I've skipped the thinning hair thing, but I found my first gray hair at 21! I am now 23 and I have found a few more. I think it's kinda cool and I couldn't care less about it but I want to make sure, this is a hereditary thing, right? There isn't anything ociated with premature gray hair besides your genes? Thanks.