> But, generally speaking, how can one explain behaviour like that?

Physiological changes between youth and old age, in particular less testosterone.

Positional changes, going from being single to having a wife and kids. Suddenly you're protecting their future instead of aggressively ensuring your own.

That sounds plausible. There was one teacher I had who seemed to have a complete personality change after he nearly died (heart problem I'm pretty certain). He went from being demon* who specialised in humiliating students to being pleasant and easy-going. The first time I ever interacted with him was in front of the public when I did my very first bit of what might be termed work experience when he loudly proclaimed to all around that he was dealing with the "absolute pits here"

Yeah, a guy I worked with was known for crazy outbursts as well. Really mean behaviour, that sort of thing. After he got married and had a kid it mellowed a lot. And that's despite his frustrations with work being the same.

I can think of at least one entrepreneur turned philanthropist who is clearly still a psychopath. Billionaire philanthropists simply have large coffers of 'good PR' money; but this doesn't mean they're actually any less psychopathic than when they were in 'entrepreneur' mode.

Being a biggest, baddest MF in the business world, he now seeks to prove himself in a new field (filantropy and „saving the world”). I suspect it’s just as ego-driven, but lucikly this time not a big net-negative on the world.