Hi Sarah, Welcome to HealthcareMagic Forum.
I can understand your Problem, which is stressful both to the family and the Patient. If you are ready to donate him your Kidney you will be needed to get yourself examined by a Nephrologist
to see if you are the right Donor to your Grandfather. He will run few blood tests and examinations on you and come to a conclusion. The survival rate
after Kidney transplant
varies from person to person and it is less if the patient is too old. Even if you become the right donor, the Doctors will consider if he really needs a transplant considering his age. Kindly discuss it with your Doctors as there are many risks involved in it.
I wish your Grandfather Good Health and Good Luck to you.