Well, from where I stand – 62 years and counting – ‘grouchy’ starts when people forget that truth – even the naked one – can be ‘exposed’ in a polite manner.

Becoming old doesn’t come with a license to stop caring about how the others feel about things.
On the contrary.
At some moment in time, each of us will reach ‘the point of no return’. After which we’ll depend on others. Totally!
For food, for water, for somebody to change our diapers…

After all, we’ve been lucky enough to reach the ‘golden age’.
How about becoming wise instead of devolving into rude punks?

‘Cause the opposite of polite is being rude. Not truthful!