If fluid intelligence is based on the ability to recognize new patterns (unsupervised learning) and crystallized intelligence on recognizing known patterns (supervised learning), then more than physiology, age alone may differentiate the two.

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?