This isn’t a new concept; it’s been around for 60 years or more. And ageism hasn’t been the problem, because age correlates with valuable experience (tech may or may not be an outlier here); sexism is traditionally cited as the problem (the argument goes, “employers think a female candidate may have or want children and therefore be less flexible”) although to my knowledge there isn’t much evidence to support this (obviously 60 years ago sexism was a problem, but afaik there’s no evidence that links it to rigid work hours). That said, there is abundant evidence that women really do want to spend more time with their children (compared with men) and therefore prefer jobs with smaller salaries and greater flexibility.

In any case, we can’t function as a society by limiting everyone’s opportunities because someone might be discriminatory. We need to address the discrimination, and we’ve made great strides as a society.

Is paying more for more hours worked on-demand ageism? If a company meeds that type of worker, it is hiring that type of worker rather than that age. Age just happens to be a rather strong proxy for reasons listed above.

I know a number of people who have done just that - taken a big pay cut - to spend more time with kids. And why shouldn't that be the case? Less work => less pay.

Thats not really what I'm saying. As a late 30 something you may be willing to work long hours, but the company may not even consider you due to your age. That is ageism.