That's the headline of this story, which I found irresistible. Money excerpt:

Specifically, it seems a growing number of people are retaining the behaviors and attitudes associated with youth.

As a consequence, many older people simply never achieve mental adulthood, according to a leading expert on evolutionary psychiatry.

Among scientists, the phenomenon is called psychological neoteny.

[...]

While the human mind responds to new information over the course of any individual’s lifetime, Charlton [the study's author] argues that past physical environments were more stable and allowed for a state of psychological maturity. In hunter-gatherer societies, that maturity was probably achieved during a person’s late teens or early twenties, he said.

“By contrast, many modern adults fail to attain this maturity, and such failure is common and indeed characteristic of highly educated and, on the whole, effective and socially valuable people," he said.

"People such as academics, teachers, scientists and many other professionals are often strikingly immature outside of their strictly specialist competence in the sense of being unpredictable, unbalanced in priorities, and tending to overreact.”

I'd read the study itself, but I'm going out to play now.