I'm pretty sure I'll be greying quite heavily by my mid-late 20's. A few have already sprouted out and my black hair has already begun to dull to a more grey/black anyway. Going grey early also runs heavily in my Mum's side of the family, which makes me happy because going bald early runs in my Dad's, and I know which of those is more preferable.

I expect to have a Matt Halpern thing going on by the time I'm his age.