But the data suggests that so-called crystallised intelligence — the accumulation of knowledge and experience — continues to build for decades. Personality traits also mature: conscientiousness (the diligence to see things through) and emotional stability (the ability to keep calm under stress), increase across adulthood before levelling off in later life.

Other skills bloom late. Moral reasoning — the ability to weigh competing principles — deepens with experience, producing sounder judgments about fairness and duty. Financial literacy peaks in the late 60s, perhaps reflecting a lifetime of dealing with bills.

• The middle-aged brain: is yours declining too fast?
how to sharpen it

People also get better at avoiding the sunk-cost fallacy, the human tendency to throw good money after bad. Experience seems to make them less sentimental about lost causes.

For now, the early signs that our cognitive health is on a downturn are the mundane and often barely noticeable mild daily memory issues, such as losing the car keys more often or a declining ability to focus on tasks and work. It might seem nothing out of the ordinary but could signify adaptations in the brain that come with negative consequences.

​​​​​​​Many studies have suggested that sleep — or a lack of it — has a long-term impact on the brain, with one of the most recent, involving 22,078 midlifers and published in Age and Ageing journal, showing that those who don’t get enough sleep in their forties to sixties could be more prone to developing dementia as they age.