I think programmers should reframe the problem. If cognitive decline is real, why would anyone hire anybody over 40? Yet there are plenty managers, politicians, doctors, lawyers, salespeople, engineers, etc. who are over 40. If you want a culture where people retire at 40, go for it. But please don't pretend that programmers are "special" in that the decline in their skills is worse than decline in skills of anybody…
I wish the author would have tried to dispel this and another myth associated with age, inflexibility. I'm still learning new things. And sometimes, choosing what I know and am strong and familiar with is a choice to expedite. It has little to do with a lack of willingness to change or learn new stuff. In fact, I'm much more flexible than I was in my 20's. Mostly because time has tempered my arrogant self-righteous self with a healthy dose of humility.