I think using the "five monkeys" parable as an argument to favour the young is fallacious.
Your tale is great, and sounds like a great experience, but I don't think it's necessarily related to the age of the participants, and to me the key here is this -
"The head of IT was there for almost 20 years"
To me that reeks of stagnation. 20 years in the same place! This person hasn't exposed themselves to new ideas, cross pollination of techniques and skills etc etc. They've become ossified and cynical, and not because they're older, but because they haven't moved around. Anyone being somewhere more than a handful of years (5?) is a red flag to me, if you're looking for technical competency.
I'm glad, for his sake, that story ends with the guy moving on!
If you're not delivering useful, production level stuff in under 5 years, even if it's not a 'complete' big project, then something's probably very wrong, IMHO.
That depends on what space you are in. In an embedded space 5 years can be half way through a products lifetime. You usually have something fairly close and mostly done in 1-2 years. But the next 2-3 years is finding out all sorts of quirks in a real world physical environment.
I stayed at one company for about 20 years. Every 2-3 years the job would radically change into something else. So I stayed for awhile. It was good for them as they could come back to me for odd decisions made and how to work around them, and for me I could work on new tech every few years. But for me on ye-ol-resume it looks like 20. My current job things are not changing like that so I will need to move on to get diff exp in something else now. The org is just not designed in the same way and it would be easy to silo yourself into a niche that melts in 10 years. You can argue with your boss to you are blue in the face about moving on and getting more challenging/different jobs. But at the end of the day they need to ship their product and they will usually not look out for you.
Three years should be enough for a decent project to go from inception to production. Realistically you will join a big project in mid-progress so three years is def enough.
I agree with grandop that 5 years is prob the time limit before moving becomes very important unless (1) you are in organizational leadership (you drive vision and with success get fu money) (2) you are being continuously rapidly promoted in a large company.
And if you don't, you kinda never get to work on more than one thing, and therefore grow and cross-pollinate ideas from different domains.
It's one of the toughest things about working as an employee if you're interested in more than one area. That's why I switched to freelance consulting, where I found the variety far more enjoyable.
It looks very likely I'm moving back to "permanent" employment soon for stability and access to more interesting "big" corporate projects that I found as an independent. (My valiant initiatives to struggle on intermittent income and use the free time to transform the hardware world into an open source hardware world don't seem to be needed any more; better people than me are doing a great job!)
But I have mixed feelings from a nagging doubt that I'll be stuck doing one thing all the time, until I have the temerity to leave the employer. We'll see, I do have an open mind and I'll give it enough time to find out, but it's at the back of my mind.
While you are right in that you shouldn't stay on the same place forever, there is definitely very huge and important lessons in staying at a place long enough that you don't only have to deliver something, but also get to maintain it over time.
I've found I actually got to stay "long enough" to maintain delivered projects much more an independent than as an employee.
As an employee I wasn't able to maintain projects longer than 2-3 years even when I wanted, due to fixed term (academic) employment contracts, redundancy, projects getting terminated due to business decisions, and reassignment to different projects.
As an independent I found I've had very long term ongoing client relationships (7+ years for one, 5 years for another so far), where they call me back to maintain their products for years after shipping.
During that, it's fine and even expected that I have overlapping newer work with other clients.
So I'm expected to maintain a number of things long after shipping, and that's what I expect to be called to do if I did a good job of delivering the project in the first place.
I think my experience of maintenance and dogfooding may be the opposite of what people think of, when they think about employees vs. independents.
While I won't ask why the multiple downvotes, because that's discouraged here on HN, I will express considerable surprise. Reading over it again, it doesn't strike me as a disagreeable comment, just another point of view about one type of working relationship over another.
I've seen a number of examples in my time, smart people who found a niche and then let the world pass them by.
Senior engineers, heads of engineering, architects, generally people who've been in one place for 20+ years, often who have been in charge of technical direction that whole time. Some of them even asked me for advice on getting out... These people tend to be respected within their organisation and have a lot of very narrow-focused domain knowledge, but because they don't move around they haven't had to think their way through any brand new challenges, or learn new techniques and systems.
It's not inevitable, but it is a pattern I've observed.
Your tale is great, and sounds like a great experience, but I don't think it's necessarily related to the age of the participants, and to me the key here is this -
"The head of IT was there for almost 20 years"
To me that reeks of stagnation. 20 years in the same place! This person hasn't exposed themselves to new ideas, cross pollination of techniques and skills etc etc. They've become ossified and cynical, and not because they're older, but because they haven't moved around. Anyone being somewhere more than a handful of years (5?) is a red flag to me, if you're looking for technical competency.
I'm glad, for his sake, that story ends with the guy moving on!