You should take some time apart from him to examine your own feelings more. With the huge age difference, you should look at whether or not your feelings for him are being confused with the feelings you would want from a father figure. If that is not the case, and you feel like you truly love him than I would not ask why he doesn't want to date you. Somethings are better left unsaid. For example, what if you ask him and he says he views you as his daughter or granddaughter? That is not something you want to hear. What if he says he doesn't think you are marriage material? He could say something that is going to make your pain worse. You should enjoy the time you do get with him and the answer will more than likely come out eventually without you having to ask.