Some animals are actually biologically immortal. That's pretty fun
i know lobsters, turtles, and crocodiles (or alligators?) are, but i'm not sure of any others.
its more like aging is a phenomena that doesnt really apply to them, because their cells replenish themselves completely with no problems, i believe. like they go from baby to adult, but never senior citizen mode like mammals do, because their cells arent replaced with lesser cells the older they get.
don't have a source, just trying to roughly quote what i remember my chemistry teacher saying a while ago.