My mom only started after her fifties.
I'm 22 and already have some strands all over my head, they are most obvious when I part my hair on the left side. My mom thinks it's weird and unatural. She doesn't mean it in a bad way, though.
I'm not sure at what age people are supposed to have gray hair, had them since I was 15
I think people (and society in general) have a tendency to associate gray hair with old age, but I'm not so sure about that. I've met people that were born with patches of white hair, so...
You tell me!