My opinion on this topic is that if we survived until we were nearly 800 years old there would really be no reason to live. If you 800 and still alive your probably just barely alive, because as you age so does everything else in your body. Your body would not be able to handle almost anything including Disease, Exercise, or even being able to Move. Also there another thing that unknown mentioned which is overpopulation. If we have everyone living to almost 800 or even 800+ there will be no room for people to live. Imagine if the people in New Jersey were living until 800...(New Jersey is a very overpopulated state already) i wouldn't have a house lol.