half marathon is ~20 KM its pretty sad that a large percentage of people cant do that. One can simply walk that much distance wihtout any prior training.

I am sure the poster meant running. Of course people can walk. That's not much of an achievement, unless you're geriatric.

You can walk it in under 4 hours. I can do it, but I can't run that much, my calves are just not trained for aerobic workloads. I don't run normally, I walk or cycle, but do not run.