Not sure if GOM was old, but he was very entertaining. He had a great sense of humor, and I miss it.
Not every old person is grumpy. If I can wax philosophical a bit, I would say that a lot of grumpyness comes from the feeling “When do the good things start?”. If you aren’t appreciative of what you have in old age (or if you truly have little to appreciate) then you don’t have much to look forward to. And anyone else who is happy or physically more able than you (and who isn’t, at that point?) just grates on your nerves.