I am 57 and think about this a good bit, and it comes up in conversations with my wife and others. Some thoughts:
I am pretty active in my church, and get to be around a number of 70+ dudes who are always cheerful, always in good humor and never complain about the younger generation. Those are my role models. They are growing old gracefully; they recognize the good in others and they realize that the world belongs to the young'uns. And they are funny as hell.
On the other hand, one of the guys I run with on the weekends likes to talk current events, and damn, I am sick and tired of statements that begin with, "In this day and age..." What usually follows is a complaint about lazy people, gay or trans, oppression of "Christian values", etc. He is gonna be a grumpy old man. (Yes, he's a Trumpy.) My takeaway is that while our attitudes affect the words we use, the words we use also affect our attitudes, so I try not to say shit like, "In this day and age," or "kids today..."
All of that being said, I suppose if I were 80, in chronic pain, unable to hear or see well, it would be easy to be grumpy. I guess I should give them some grace.