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.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.