12 km/h isn't particularly unachievable. I'm middle-aged, heavily built, run to and from work a couple of times a week and otherwise do no cardio exercise. I'

12 km/h isn't particularly unachievable. I'm middle-aged, heavily built, run to and from work a couple of times a week and otherwise do no cardio exercise. I've built up to that kind of pace over a couple of years.