> Software engineers didn’t just disappear after age 40.

At the end of the 90th and beginning of the 00th ("dotcom bubble") it was a common saying that if as a programmer, when you are 30 or 40, you don't have a very successful company (and thus basically set for life), you basically failed in life; exactly because "everybody" knew that programming is a "young man's game" (i.e. you likely won't get a programming job anymore when you are, say, 35 or 40 years old).

So,

> Software engineers didn’t just disappear after age 40.

is rather a very recent phenomenon.

Enter the carousel. This is the time of renewal.

> At the end of the 90th and beginning of the 00th ("dotcom bubble") it was a common saying that if as a programmer, when you are 30 or 40, you don't have a very successful company (and thus basically set for life), you basically failed in life;

This wasn't common anywhere except for maybe the Silicon Valley bubble.

The rest of the US and even the world could see that not having a very successful company of your own is to equal to being a failure.

> At the end of the 90th and beginning of the 00th ("dotcom bubble") it was a common saying that if as a programmer, when you are 30 or 40, you don't have a very successful company (and thus basically set for life), you basically failed in life; exactly because "everybody" knew that programming is a "young man's game"

That seemed commonly held among folks participating in the dot-com bubble. Plenty of people had been doing it for decades even as the bubble was growing.

> Software engineers didn’t just disappear after age 40.

>> is rather a very recent phenomenon.

Not really. It's not that they disappeared, it's that they're a small fraction of the overall SWE population as a side-effect of how much that population has grown.