Ageism is real. It's not some sour grapes of under-performers who let their skills decline, or move or think at a dotard pace. It's essentially "We don't want anyone old because old = bad, new = good."
I think it is a lot about under-performers that want to hang onto their "years of experience" as a selling point and being angry that there is not much of a market for "years of experience" only.
Maybe they were not under-performers 10-15 or 20 years ago, but if someone gives 20 pages of resume and most of it happened in 90's I would not be interested. Because it is quite easy to see such person is hanging onto his past performance like Al Bundy to his 4 touchdowns in high school.
If someone would be 50yrs old or even 60 but his last couple of years are taking most of resume and they did interesting work at that age I would be curious to talk to such person.
It is not that they would need to have latest frameworks or libraries listed on the CV. It is more about if they did meaningful work in last year and not that they did meaningful work 20 years ago and now they are just hanging around doing whatever.
So my resume concentrates on the last five years, with the prior 30+ being mere bullet items, in the event you want to ask. You are correct that no one really cares about what you have done outside the last five years.
This is also true. Definitely can't slack off on the couch with a hand in their pants. Even someone with little experience can become perpetually stuck starting at the beginning of their career in low performance if they don't push themselves towards excellence. Slacking off at any point leads to a downward spiral of decay.
