Jonathan Rauch isn’t alone in preferring his 50s to his 40s:
Studies show quite strongly that people’s satisfaction with their life increases, on average, from their early 50s on through their 60s and 70s and even beyond – for many until disability and final illness exact their toll toward the very end (at which point it’s hard to generalize). In a 2011 study, for example, the Stanford University psychologist Laura Carstensen and seven colleagues found that “the peak of emotional life may not occur until well into the seventh decade” – a finding that is “often met with disbelief in both the general population and the research community,” despite its strength. …
Rauch adds, “In my own case, what seems most relevant is a change frequently described both in popular lore and in the research literature – for some reason, I became more accepting of my limitations”:
The idea that the expectations gap closes with age has recently received some empirical backing, in the form of fascinating findings by Hannes Schwandt, a young economist at Princeton University’s Center for Health and Wellbeing. He used a German longitudinal survey, with data from 1991 to 2004, that, unusually, asked people about both their current life satisfaction and their expected satisfaction five years hence. That allowed him to compare expectations with subsequent reality for the same individuals over time. To his own surprise, he found the same result regardless of respondents’ economic status, generation, and even whether they lived in western or eastern Germany (two very different cultures): younger people consistently and markedly overestimated how satisfied they would be five years later, while older people underestimated future satisfaction. So youth is a period of perpetual disappointment, and older adulthood is a period of pleasant surprise.