physical deterioration doesn’t really become evident until after/around 30 (the end of the plateau). neural development happens well into our 20s, with a long plateau into our 30s and a gradual decline after that (only becoming substantial around retirement age). growth from experience seems to be substantial into the teens, where it hits an inflection point and starts to decelerate but still climbs, albeit more slowly over time, well into our 40s at least but possibly our whole lifetimes.

we’d still get the most bang for buck if our age was ‘frozen’ in the late 20s because experience would still accumulate regardless, but we’d have maximized the combo of physical and mental growth. it’s only obvious in retrospect how immature we are at 18, both physically and mentally, or even at 25. that’s why sports is such a neat test bed, because it taxes both facilities enough to tease out these otherwise unnoticeable dynamics.