This is a funny thread, because this is exactly my plan.
Right now, I'm in my 30s and the grey hairs are sprouting more often & in my temples. They aren't noticeable unless someone is standing way too close for comfort. But I figure, another year or two, they will be and it'll help me catch up more to my age.
I've even thought about deliberately dying more hair grey if I start to get pissed off about being read too young. I don't think I'll ever get to that point, but yeah, I've considered it.