What is a high low-flexibility salary?

I'd guess there should have been a comma there, i.e., "high, low-flexibility salary." I'm young and don't have a family to worry about; I can work really hard, advance faster, earn more, and still have a little free time for teaching myself more interesting stuff. I have a salary which is higher than others who fill the same role, because my flexibility is less. I put more time into my job and available more, so I am compensated accordingly. I think that's fine.

Work 60 hours a week if you must, but I don't see the point of high availability.

Developers are not paramedics, our jobs should not require instant availability and the systems should be stable. There is a difference between being productive and being available for random unplanned bullshit.

Maybe not, but if someone is willing to pay you for it and the deal is agreeable to you, then good deal. If the deal isn’t agreeable, then negotiate a better deal. If you can’t negotiate a better deal, find a new job, if you can’t find a new job, then your current deal is optimal. This applies where we’re talking about working more hours or less flexibility. It’s economics all the way down.

The problem with this mentality is that it leads to ageism and encourages companies to hire 20 something's who they expect can bend to their schedule. They are going to assume anyone in their late 30s or older has kids or wants kids, so won't be able to be flexible enough for the role.

Even though CVs don't (at least in my country) have DoB you can infer it from years in education. You might not even get a chance for an interview to say "I never want kids, I just want to work hard".

Let's pretend all jobs are like this, where flexibility pays more, if you do ever plan on having kids, could you afford and would you be willing to take a big pay cut so you can spend time with them?

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.

That’s unclear on my part. Prior to that sentence, I noted that some salaries are high because employers are effectively paying for the employer to be available at specific times, even around the clock. So these low-flexibility jobs have high salaries.

We'd need to identify these positions somehow - at the moment the weird hours and overtime seem to creep in insidiously. Few are going to label themselves low-flexibility.