I think that this is a better and more constructive article than the various other age-related articles drifting around. It may very well be that the level of fluid intelligence is the real issue, and that this level is partially inversely correlated with age because, as time goes on, more and more people stop playing, and few ever start playing again once they've stopped.

Many people probably stop play-like activities because they consider it to be wasted time, much like sleep, and so it gets the axe when time is scarce. Perhaps if they realized its importance, they'd make time for it.

I think a culprit in age-related decline of fluid intelligence is Careerism.

I don't mean the idea that you should take your career seriously. That would be lower-case-C careerism. What I mean is the idea that you should evaluate every aspect of your life from a point of view of "will this get me a promotion" or "will this get me a better job?"

That not only causes you to stop playing, but in my experience it kills all creativity dead.

I complete agree.

Heavy-handed priortization also causes less fluid thought.

I'm really glad Silicon Valley shops tend to have a playful culture. It makes it easier to fight for it where I work.

Some of the more creative people I've known seem to be the same ones that blur the lines between work and play. They'll have an interest in something and dive into it having a great time. They're constantly thinking, analyzing, enjoying what they're doing, looking at every angle of doing something. (sounds like Apple?) They're not afraid of much of anything either, including some failures (which they also learn from). They're not going through some memorized motions, they're heavily involved.

I guess that's where they play side of it ties in... heavy involvement, and the happy-chemicals that go with fun/play help to more easily form mental pathways. Disliking what you're doing, being completely bored/mechanical or having excessive levels of anxiety tends to shut one down mentally.

Work hard and play hard

Does playing video games count? I have plenty of those under my belt. :)

Yes [1].

[1] Rosser JC Jr, Lynch PJ, Cuddihy L, Gentile DA, Klonsky J, Merrell R., The impact of video games on training surgeons in the 21st century., Arch Surg. 2007 Feb;142(2):181-6; http://archsurg.ama-assn.org/cgi/content/full/142/2/181

Awesome! All those playing are not a waste of time as everyone has berated me.

Well great to know. But I thinks they are some other factors apart from Fluid and Crystallized intelligence.