> In men, graying first occurs in the temples and sideburns. It spreads to the vertex and rest of the scalp involving the occiput the last.

My graying started when I was 15 and first appeared as a single silver strand at the center of my hairline. At 28, I now have a cluster of them in that center spot, as well as diffusely all over my head, including the occiput. I think my temples and sideburns were actually relatively spared.

Also of interest to me: once in a blue moon, I shed a hair that appears to be reverting from gray back to pigmented -- it's gray close to the tip and black closer to the root. I wonder what factors might cause this reversal.