There were recent tests (in France I think) in schools where 50% or something could not run 1 km (sorry I don't have the details on mobile). These are children who have infinity energy (source: parent).
A typical adult won't make it to 1km (source: going back to sport and dying on a 2.5 km run)
I'm... dubious of this. At 39 I started running, for the first time in my life, ran 5km, didn't actually die, and went from there. I'd think most adults could manage 1km, anyway.
I used to play volleyball a lot at the university, and then at a business league (we were horrendous, but anyway :)). Then I travelled a lot and let myself go.
So I started to commute to the office by bike, about 15 km each way, 5 days a week for two years. I had a puncture and decided to run the remaining distance (about 2 km) because I was late. After 500 m my lungs were on fire.
55 now, I restarted this year sport to do the smallest existing triathlon. I was already biking a bit and "just" have to do the swimming and running. I am at my 10th or so run of 2.5 km (I try to do it 2 times a week) and I am dying several times on the way. The fact I make it back home is religiously miraculous.
I am not an athlete, far from this. I am not the extreme obese either. I am somewhere in between, like are most of the people I know (of different ages). I do not see them running 1 km strong (let's say right above trotting)
Ah - and I did the whole battery of medical tests to make sure that I will not literally die when training. I am in a very good shape, heart wise.