When I became a grandparent for the first time, I was 47. Being a grandparent is a LOT more fun than being a parent - discipline is Daddy's problem. I'm not only allowed, but expected to spoil them.
I met a lady in a retirement village who carried a cane under her arm, not leaning on it - it was "to stop bad men from trying to steal my purse". She refused to have a walking frame, those were "for old people". Pride of place on the mantelshelf of her living room was a telegram from the Queen, so she was at least 100, but didn't consider herself to be an "old person".
Good for her! There are two parts to aging: your actual age and the age you feel. I don't feel 77, don't act 77 and no one I meet for the first time thinks I'm 77. I try to keep up with what the younger folks are doing, with what is going on in the world around me and I don't speak with the reedy voice associated with an old person. I have also been blessed with a round face, which generally makes one appear younger than they are, and I have few wrinkles on my face. Good genes, I guess. :)
You can be old without being decrepit or demented. I consider 70 to be old and yet most 70-year-olds are still vital, productive, interesting human beings with many good years ahead of them. Being old is something to celebrate. Let's stop being ageist and appreciate the benefits of our experiences and accomplishments.