Agree with Jiejie. I'd recommend Japan if it's end of April or May. Later it will be too hot. Long flights can be extremely debilitating for someone of your grandfather's age so Tokyo is good because it's a lot shorter than SE Asia. Lot's to do. Good public transportation. Wide variety of food. Good medical, etc. Also there are plenty of reasonably priced accommodations if you don't mind it being a bit spartan. *A is probably you're best bet for scoring an award ticket, but you'll need 120k miles for J.