I think "normal" would not be a good description but certainly neither would "rare". Lots of people start balding at 30 or so. My dad did and I always figured I'd bald early but it hasn't happened. As Dave said, grey is better than gone. And hey, look at Anderson Cooper. He's 47 but that didn't start yesterday, so he's one example.
It's not common at a younger age, but it's nothing to be worried about. I'm 14 and I have one or two grey hairs...yes I know not great but hey. Basically it means you have a high testosterone. Google it, It'll tell you more ;)
What's weird is that grey hair can turn dark again. Grey hair can be caused by health issues, including stress, some medications. I have hairs that turned grey, then just turned brown again, not gradually either, suddenly. I have the hairs to prove it. Makes you wonder if when we understand how things like this work if we will be able to manipulate if we turn grey.