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 always assumed that it was something to do with people getting increasingly frustrated with the struggle of keeping up with stuff.

Chronic pain probably plays a part too. I know I get grumpy and miserable when I'm unwell or in pain.

I've attributed that to a decreased ability to deal with novel situations as we age. E.g. the world behaved differently than I was expecting.

One thing it's definitely possible and important to intentionally keep exposing oneself to!

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.

But all the objective bullshit still existed when we were younger! And it didn't bother us as much then.

I was much less aware of it when I was younger. Ignorance is bliss.

Spot on. People learn to recognize it from miles ahead and in now what's up.