I teach in a private boarding school that takes almost all my time. In my school, night prep is like day time because of the lighting system available every where. Honestly. I hardly have time for myself. But recently I notice gray hair all over my head, when I ask friends about it they told me, it is the effect of excessive working condition, am in my late 30 now, by geneology my Father at 45 don't have gray hair neither is my grand father. What my friends said could it be true?

Yes. It can biologically proven. But no time

I believe it does take a look at the likes of Obama, Goodluck Jonathan, Pep Guodiola, Jose Mourinho etc, although, I don't know if scientist have proven it boyond reasonable doubt.

excessive stress can result in pre mature grey hairs, enjoy it, some ladies think it's sexy.