Kissinger doesn't look that more healthy than trump. I think it's just that Kissinger is actually aware of what he has done and the fear of hell is keeping him alive.
If you Google Kissinger you get a bunch of pictures from a bunch of different ages.
Besides, once you reach 80 you basically roll a d20 to see how much longer you get to live. You can be the healthiest man in the world as still roll a 5.