As someone who actually has worked as a programmer on the far side of 40, let me assure you that yes, older programmers have value. Your perceptions are not wrong. But that said, the article is right. The people who do the hiring and firing do not care about what you care about.
As the article noted clearly, the marginal benefit of an older engineer has to exceed the marginal costs. And if we’re being honest, the fact that a graybeard can use tcpdump without reading the docs carries little marginal benefit. Guess what, kid? You’ll figure it out, and you’ll do it quickly enough that the total cost of your learning won’t really compare to the cost of hiring me.
That’s why you see lots of anecdotes about the value of older engineers, but lots of articles from older engineers who know that the discrimination is real. And this is coming from someone who has managed to “stay relevant” a lot longer than most software devs.