But as a programmer in his 50s, when I have personally encountered age discrimination, it's been instant. It wasn't just a thumb on the scale or issues with disparate impact, it was an obvious and clear reaction the moment I walked in the door. It's always stunning when a very pleasant and productive phone conversation becomes immediately hostile when somebody sees my face.
On the other hand, those moments have relatively been rare, and this industry is currently so competitive that they register as "I dodged that bullet" rather than anything truly harmful, although it's definitely been enough for me to see the words "culture fit" as having the definition "we practice illegal discrimination".
BTW, whenever these articles show up on HN we always seem to assume that "tech worker" means developer, but it really refers to everybody: support, manager, tester, etc. If you're a developer, there's tons of ways to keep your skills strong. But the support person who's been keeping a Sybase instance running for the last 20 years or who maintains some spaghetti netware system doesn't necessarily have any marketable skills. There's a lot of people whose skillset is essentially "I've been here a long time".