I think he is referring to the age gap, not just teachers, although with millions of teachers over the decades thousands is within statistical possibility
Citing all of humanity’s history…I think the young teen/young adult age gap has happened far, far more than thousands. Especially since a little over 100 years ago when men and women would get married at 13. 14, 15 years old. In an agrarian society, more hands equals more work. I’ve done genealogy research and it was common to have over 10 kids. That **** isn’t happening if you’re starting at 25. It’s estimated that humanity has had 117 billion people. I would say that hundreds of millions is a much more likely number than thousands.