Usually when I come to write a story, the central character picks themselves. However, I'm working on a new idea where that hasn't happened. I could go with anything from a teenage boy to a married woman to an ageing widower. While the concept would be the same for each of them, the telling of the story would be completely different. And of course, this all assumes I write it from the point of view of one character instead of many.
How do you go about choosing your heroes? Do you do so with a target market in mind? Is there any kind of viewpoint character you wouldn't or couldn't write?