Use it or lose it?

One of the worst things about getting older is becoming stupider. It's not, I'm afraid, just a matter of losing the edge off your memory. The gruesome fact is that, on standard tests of raw intelligence which do not rely on stored up knowlege or well rehearsed mental skills, from the mid-20s onwards your mental abilities steadily decline. Now 90% of jobs are 90% routine, and age may confer advantage to the routine via long experience and hugely practised skills, but non-routine problem solving is better done by the young. Hence most mathematicians have to make their names and find their chairs in …