Does that imply that it also is part of character traits? As in use empathy, become emphatic, stay in a non-emphatic environment, your brain degrades you to a sociopath?
I hung out with a friend recently I had not seen in close to a decade. He was at one time my closest friend and seeing him was kind of uncomfortable and enlightening. I saw sooo much of how I used to talk and act still in him that it really had me wondering how much of that I'd gotten from him versus the reverse.
I think it has more to do with getting desensitized to things the more you're exposed to them. With age you get more and more exposure to everything emotional and lose the strong reactions.
Add to that some frustration from not being able to keep up with things, health issues, no one "young" having time to hang out and your friends dying all the time and I'd be grumpy too. You were once a stallion taking care of everyone and now you worry about falling in the shower because you occasionally lose balance for whatever reason. And you know it'll hurt like a bitch, you'll break something and it won't heal for a year. It's quite humiliating.
I am definitely grumpy. What makes me grumpy is the fact that society keeps banging its head against a wall for no good reason.
There is everything there for growth, and yet I see none. I get very tired of knowing well what the boring, selfish reaction of the person I encounter is going to be. I am sure I do the same thing - and don't change much compared to what is available to me to make changes. I do not lead by example at all the way I would like.
Nonetheless, what makes me grumpy is lack of change, not the superficial appearance of change with which technology distracts us. Moral growth would be so refreshing to see, but I see none of it - despite virtue signalling as a veneer from all parts of society.
Said more colloquially, a lot of older people just grow tired of all our bulls*t.
As with most research around our scientific understanding of intelligence, I assume this only scratches the surface.
There may be something to your comment.
There are trajectories of personality traits over the life span, I would hesitate to extrapolate them based on the trajectory of cognitive abilities though. One of the known life span emotional/personality trajectory is positivity bias, older people tend to be more positive. It is sometimes framed as negativity avoidance, that is older people tend to ignore negative things more often.