So the middle-aged brain is a triumph. Although the sensory information entering it is becoming ragged, and its internal processes do not work at quite the speed they once did, this does not seem to matter much. Quite simply, the middle-aged brain is at the height of its cognitive powers and whether you subscribe to the 'summit euphoria,' 'trouble ahead' or 'deceptive plateau' view of that feat probably depends on whether you are an optimist or a pessimist. One thing is clear, though: the genetic developmental 'clock of life' still ticks inside the middle-aged brain, and it drives a radical restructuring of our thought processes, encouraging our brains to develop new ways of working well into our fifth and sixth decades.
It makes sense of middle age to be a time of cognitive excellence - the brain allows middle age to be humans' most productive time, as well as a time when we are best able to convey our culture to others. p.108-9