Anecdotally: I'm a week away from turning 39 and I don't feel I've lost any "raw" mental ability, but actual performance has gotten more challenging because I'm

Anecdotally: I'm a week away from turning 39 and I don't feel I've lost any "raw" mental ability, but actual performance has gotten more challenging because I'm pulled in many more directions at once. Very few people face the same level of obligations at 20 as they will at 30 or 40. There's also the Dunning-Kruger effect: the better you get at something, the worse you feel you are at it... presumably, all of us have made strides towards mastering our craft in the last 10 or 20 years....