I have written about what makes a runner in the past. It took me a few years of running before I would consider myself to be part of the group. That was just my personal inability to see myself as an athlete.
I love John Bingham's take on it. There is no membership card to get. If you run, you're a runner. He should know, too. He's written for Runner's World and Competitor magazines. He's also written several books on running. His pacing looks to be about a 15:00 or slower mile. He's still run more marathons than I can imagine, even though he didn't start running until his 40s.
Bingham says, "Through running, I create myself as I have always wanted to be. Nothing in my experience was as powerful as crossing the finish line of my first race. With that single step, I overcame a lifetime of unkept promises to myself."