My only remaining grandparent is 85, and it is tough to see her struggling to get around - arthritis is her poison. It is crushing to see someone you love in pain.
We should all be so lucky to make it 83 years on this planet, and I am sure that anyone who has done so has had a very full life. I can assure you that your love and presence in your grandfather's life during this time is one of, if not the most pleasurable and appreciated aspects of his existence. Grandparents, especially close ones like it sounds is the case here, love their grandkids in a way that not even parents and their own kids can touch. Your being there physically, on the phone, or however else is a priceless gift to this man, and you will be glad that you spent this time for the rest of your life.
My thoughts are with you. Best, ©