For me they normally happen, these career crises, often, actually, on a Sunday evening, just as the sun is starting to set, and the gap between my hopes for myself and the reality of my life starts to diverge so painfully that I normally end up weeping into a pillow.
The great secret that all old people share is that you really haven't changed in seventy or eighty years. Your body changes, but you don't change at all. And that, of course, causes great confusion.