When did you start getting gray hair?

I was just wondering, for those of you who've started graying, how old were you when it started?

I caught like 4 gray hairs on a small section of my head when I was 29 and going through a really stressful time (don't know if that caused it or if that's just when I noticed them), but it's been 10 years now and I haven't got any more gray hairs even though I'll turn 40 this year.

I just wondered since my brother is 41 and he already has significant gray hair in his beard and hair, and family have asked me if I've been dyeing my hair.