Our dog hasn’t gotten that bad yet, but I am keeping a sharp eye on her for when she starts being aggressive..................
I’ve only had that one dog become mean in their old age; my GSDs and my Rottie just got sort of confused towards the end.
Our Welsh Terrier went full Biden at fourteen. He remained loving and never got grouchy. He slept all day and in the evening he was a “sundowner.” He was confused, we would find him just standing in a dark walk in closet. The sad part was most of his personality was gone. One day he squatted in front of me gave me a pitiful look that said “sorry I don’t know what I’m doing” and peed on the living room carpet. I took him to be euthanized an hour later.