Noticed my first grey hairs a few months ago and it's become more since then (I'm 28). Hardly surprising since my dad's hair were mostly grey when he was around 25, so I figured the same would happen to me. Probably not having kids yet delayed the process a bit, although being a teacher isn't exactly helping either
I have absolutely no problem with having grey hair, I'm just glad I still have very full hair. A couple of friends of mine are balding and I definitely prefer turning grey.