Immortality and extreme life spans are not plausible. You body's set metabolism controls your organ biological life and your genome dictates against rejuvenating internal organs. Change your genome (which you can't do) could only be applied on genetically engineered baby, and it would no longer be a Homo Sapien it would probably be on its own evolutionary branch. In order to grossly prolong life you would have to go with old school methodology and like a old car keep replacing the used parts as they break down, by growing every human organ with a neutral genetic pattern so no rejections manifest themselves. Even then once your body is taken care off, your brain is not immortal either. Every hour thousands of brain cells die, so you would once again have to create some kind of compatible biological brain cells grown in vitro, which is very science fiction. Right now if you took some kind of substance (drug) that could grossly slow down your metabolism like beta blockers for the rest of your life i bet my best pair of Spiderman briefs, you could live for a extra 10-20 years. But you would live those years with the metabolism of a turtle, cold all the time, eating a very low caloric levels and have no fast motor or sensory reflexes or thoughts. I think the closest we will get to using these sciences if by every baby in the future using artificial fertilization that will act to screen the genes for heritable diseases (assuming we find out all the genetic combinations for them) - so less diseased death = a mean longer life for the average person. I could write a lot more but this looks like plenty and I have a hankering for a spankering ...