Strangely enough, facial hair usually turns grey before hair on the scalp.
Stray gray ones showed up on my chest first, then moved up. Just remember there is an old French expression that says, "Never pull a white hair out because ten will come for the funeral."
It started at the temples for me and slowly crept is way around my head. When I shaved I was pretty much completely gray. On the rare occasion when people ask me why I shaved my head I tell them that I went to my barber and told her that I wanted to get rid of my gray hair and this was the result - gray hair is gone!