I've been an endurance athlete most of my life, running 100 miles at 17, a 5:30 mile at 50, and lots of other stuff in between. I know that a 9min/mile pace is "easily achievable" by many folks, which is why I noted that millions or billions of people could do this. Nevertheless, I think it is really important to not overstate how achievable this is - there are many more people who could not do this than could, I think.

FWIW, that now includes me, as a 62 year old. I can hit 6:30 pace for 400m, but find it almost impossible to get under 10:0x for a mile. And that's even after 6 months of training for a 50 mile trail race.