I understand (a little) that there are biological clocks and reason that after a certain amount of time organisms die. I'm wondering if that is something inherent in our DNA or in biology/chemistry in general. EG, is it possible that there could be a complex organism that would not die and would just regenerate it's cells In Perpetuam? I'm specifically interested in mammals and even more specifically interested in humans. But, I would be interested in hearing about other organisms like bugs, fish, plant, algae, etc.
I'm not asking if this practical, do we know how to do this, etc.. I just want to know theoretically if living forever is biologically possible, as far as we know. If not, is there an estimated upper limit?