I think this answer varies with everyone, as does how to interpret a book and so forth.
I am a very black or white person so the grey area is hard for me to imagine.
When do you consider yourself a runner?
For me, this answer is simple. I am NOT a runner. I ran track in highschool, I was a 400 meter girl. I still never felt like a "runner."

I have a time goal in mind (as we all do) but I don't think I'll ever achieve that. If I ever do, maybe I will call myself a runner. Are you a runner if you only run marathons? If you just love to run? If you can run sub 6 minute miles? If you run over 100 miles/week? When are you a runner?
Since I cannot answer any of these questions, my answer remains the same, I am not a runner.
What do you guys think?
For some reason, I have always considered myself a cyclist. Let me elaborate here, I am NOT the fastest cyclist in the world. I will say that most of my victories in triathlon do come from the bike portion but I am not the fastest.
I think that I just love biking and I love my bike. I never even thought twice about calling myself a cyclist or when I should start? I know that road cyclists may disagree, but I still consider cycling my love and passion.
Maybe that is what happens when you love to run? You just call yourself a runner?
Ahh, the mysteries of life!