It does seem like sometimes we realize too late what we have missed. If I could go back there are so many questions I would ask my grandparents or parents, unfortunately I won't be able to do that. What you will need to look at is who is still around that you would miss if they were to die tomorrow and make sure to spend time with them now and not wait until it is too late. Be there for your father. I'm sure that he could tell you stories that would help you know more about your grandfather. Relish in the stories. They will help you through.