I've been seeing this "you can't find a job after 35/40/45" meme on HN pop up frequently. This literally can't be true: our economy would have collapsed by now

I've been seeing this "you can't find a job after 35/40/45" meme on HN pop up frequently. This literally can't be true: our economy would have collapsed by now if a large fraction of our population were forced into retirement at 40. If everyone became unemployable at 40, 1/3 of the population would be supporting the other 2/3. Yet instead we see low unemployment. I don't doubt that age discrimination in tech is real, but I'm pretty sure comments like this are way overstating it.