> Fluid intelligence or fluid reasoning is the capacity to reason and solve novel problems, independent of any knowledge from the past.
I'm not saying that isn't not important in the disciplines you just mentioned. I _think_ however, that it's more important when you work on something that is meant to be "disruptive". I don't think that for example carpentry necessarily belongs to the same job category.
A lot of old people here seem to be clutching onto "experience" but it is heavily overrated in a society/industry based on learning new things.
Younger people have more potential ( intellectually and physically ), they can work more and they are able to learn new things far more quickly than old people. Add to that the fact that young people are already immersed in new technology and they fit more naturally in a younger tech work force.
It's like asking why magazines seek younger men and women? Because it works and it's the optimal solution.
Also what level of impairment are we talking about here? You make it sound like everyone over a certain age is a doddering old coot. :)
http://news.mit.edu/2015/brain-peaks-at-different-ages-0306
I also didn't mean to sound like that :) I'm on the "decline" side and even though I'm not necessarily happy with that, I also understand that you can't cheat biology.
A lot of information can be found in psychological literature touching on Cognitive Psychology.
I think OP's article is talking about people between the ages of 35 and 60 not being able to see ads.
What is more likely is that more experienced workers have higher salary requirements and are less likely to work 90 hours a week.
Salary and work-life balance expectations definitely play a huge role in this phenomena - I'm just pointing out that there might be other factors too - factors that people often reject up front because they feel uncomfortable with them.