We now know this is simply not true. Your brain — every brain — is a work in progress. It is "plastic." By Michael Merzenich, Ph.D. From the day we're born to the day we die, it continuously revises and remodels, improving or slowly declining, as a function of how we use it. If a brain is exercised properly, anyone can grow intelligence, at any age, and potentially by a lot. Or you can just let your brain idle — and watch it slowly, inexorably, go to seed like a sedentary body.
Most older brains, by the way, are neglected. They are therefore slower and less accurate, and do poorer job recording useful information and controlling their owners' actions.
Tune in Wednesday Feb 4 At 7PM for the rest of the story.