The soul, your whole being, is the brain-stem, not the brain, some children are born without a brain and still have a personality, so it`s located in your brain-stem, or the whole thing, to say, the problem with living forever, is that your soul ages, common misconception is that the body ages, but it`s not true, the body is maintaned by cells who are automtically run by DNA, it`s your being that ages, the soul, when that happens, the body follows, problem with maintaining the cells in your soul, is that if you replace them all, it wouldn`t be you anymore, so you`re stuck with the same cells all your life, if you for example, drink alot, or are stressed alot, working hard, and so fourth, your soul ages faster, especially if it`s negative stress, you stay younger if you live healthy and workout normally, use your body normally, but the soul ages, so there`s not possible to live forever, the more complex you are born, or, intelligent, to say, the longer you live, that`s why animals lives shorter, the more complex you are built, the longer it takes to break you down, the same goes with plants also and trees