Coding does matter, but most companies can only extract a limited amount of value from code, due to various dysfunctionalities in how they operate.

Being a good coder in such a company could be problematic, because they won't be able to recognize ability or benefit from the difference in skill to an average coder. These companies will treat programmers poorly, will try to save costs, outsource, etc.

I don't get why you claim that younger people will replace 40-somethings. It's not like the older devs will break outside of the warranty period.

Because I'm not seeing younger developers complaining that they are being replaced by older ones. What I am seeing is older developers complaining that they are being replaced by younger ones.

If they want a big salary and can't deliver enough value for the company or the company can't extract enough value from their skills (see above why) they might be let go, but this happens in countries with poor worker protection, like the US.

Companies in EU countries have the opposite problem, they can't easily dismiss employees, even when perhaps justified.

I wouldn't want to work in the US, it's too darwinian. A company shouldn't be able to dismiss an empoyee just because there's someone cheaper available.

Yep, but perhaps to phrase differently: once you get to a certain point, you build a reputation and business network. People usually want to work with you because they know what to expect (in terms of professionalism, code quality, etc). There's also value in that, whether as a programmer, manager and/or consultant.

If you are 60 and just won the Nobel prize and you are still thinking about your skills in terms of "I can win a Nobel prize", then I have very bad news for you. There are hundreds of people (https://www.nobelprize.org/nobel_prizes/lists/age.html) who can win Nobel prizes at ages younger than you.

Or: this argument is meaningless because it's assuming more supply (of someone like you) than jobs (and perfectly informed employers for that matter).

I'm not seeing those winning Nobel prizes complaining about them being fired from a job because they are old.