Mental speed is high until age sixty
Over the years, I have become convinced that much of the observed age-correlated cognitive decline in people younger than ~70 results from voluntary life choices, such as settling into fixed behavioural patterns (e.g. doing the same thing over and over for decades) and lack of exposure to new stimuli.<p>It's the case for some physical activities as well: almost all people's actual performance degrades way, way faster, than their potential peak performance.