As someone well past "peak" fluid intelligence at this point, I always hate reading research like this. "Crystallized intelligence" and "emotional intelligence" are the consolation prizes no one really wants.

I'd rather we instead perform research to identify how one might reverse the decline of fluid intelligence...

Isn't it about accumulated human capital (aka social networks) and experience more than anything else?

Youngsters know no patterns so they can't match new events to known ones. Oldsters know that most seemingly new stuff is not really new, it's just the same old stuff, so they reduce the cost of thinking and reject the noise by adding the new unlabeled event to an existing cluster rather than creating a new noisy one. That's wisdom. But that's also a behavior that will inevitably increase as we age and our clusters establish themselves and prove their worth.

So aren't those two forms of intelligence less about a difference in brain physiology and more about having learned to employ common sense?

Aside from the lack of randomization, you have obvious validity problems. The interpretation of nebulous words like "reasoning" as being accurately measured by e.g. accuracy on Raven matrices (construct validity?) and younger participants having been primed by recent test-taking experience while real-world reasoning skills aren't really reflected - it's all quite specious.

Real-world decisions are value-laden and constraint-laden! "Intelligence" does not mean "maximizing abstract pattern detection". If you keep your brain active with a wide range of creative, interesting problems, you will be fine apart from neurodegenerative diseases, which have real effects.

https://pubmed.ncbi.nlm.nih.gov/30211596/

In my case I was quite good with numbers in my 20s, not any more in my late 40s. But I believe now I know the world best in my life and that is increasing.

Where I worry is that these papers will be used to justify ageism. Looking through these comments, there's quite a lot of positions being bandied around that I've heard justify some truly atrocious hiring/firing decisions before, and we need to be cognizant of the reality that age alone is not an indicator of success or failure for a given role or task. It's helpful to keep looking into this, but we also need to be aware of our own biases.

Sure we can generate syntactic and semantic descriptions endlessly but to use software as an example, we made a lot of the same things that look different only in the symbols used.

Ansible and Chef. Terraform and Pulumi. Ruby and Python. Windows and Linux. Burger shack 1, burger shack 2. They all solve the same problem.

Being able to generate semantics endlessly does not upend our daily patterns and routines. Life on Earth is pretty obvious.

Still in the game :-)