Ok, i'm 17 and ive read almost zilch on life expansion. I have read 0 of the other theories here, and I am speaking from a totally curious perspective, and I know it will sound completly ridiculous, so go easy on the bashing
Free Radicals (I also know almost zilch about these things) seem to damage Mitochondria (all I know is it starts with an M, and they are located in the body) so would the answer to living forever (or atleast a long time) be growing new mitochondria (is that possible) via stem cell or something, and then putting new mitochondria into your body. Would this theoretically work, if you had the knowledge of how etc etc.