We don't know, in that much detail. Broadly, as I understand it there's some evidence that you "use it or lose it". Flynn's book "What is intelligence?" discusses this - part of his argument is that IQ depends to a large extent on environment and it's really current and recent environment that matters, not e.g. early childhood environment. My father does Killer Sudoku and calls it his "anti-dementia exercises" FWIW!

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