Depends who you ask.

You my boss? It’s the work. And I was in IT.

Wife? The kids.

Kids? Because I like the smell of White Out^TM^.

Just kidding. I don’t actually say those things, I make better jokes but I can’t remember them anymore because my face caught up and nobody asks anymore.

In my case it’s genetic. I started getting greys in my early 20s and was fully grey by 30. This happened to my father. This is seemingly happening to my son. But only one of two biological sons yet the other has curly hair like my father that me and the other platinum child don’t have at all.