it could exist or at least much longer lifespans and could happen very soon, we are starting to discover the chemical processes of aging in our cells, and have already began to fight this aging process of our cells not being able to dispose of damaged protein. In fact back in 2008, august I believe, for the first time ever scientists were able to stop the aging process all together in the livers of lab mice. As we further refine this and with human organs, we can eventually slow the aging process if not stopping it all together. So it very possible that in the near future the average human could live to be 200-300 years old instead of a max of about a little over 100 now.
This of course present problems as well as it presents promises. Population of course is one. About the only option would be very limited births, for example say one per parent and can only become pregnant at a very late age so that their child pretty much is there just to fill their spot when the die. As children for most of us is the only reason for living at this current day and age, in a time where you can choose to live much much longer and age much slower, sadly to say the majority of humans would choose that for themselves over having children.
So will immortality happen? maybe... will much longer lifespans happen? very probable. When it does the real question is though which will you choose, and be honest with yourself... if you had the chance to slow the aging process down alot and live to see things far beyond what you would be able to now, would you do it? I know I would for one.. I love my kids very much and I love my own life very much as well. No one really wants to die, especially if you dont know what if anything lies after life. I would choose to stay alive as long as possible, be with my kids as long as possible.