I have heard that a fish never stops growing.....................
I’ve also heard that either alligators or crocodiles are essentially immortal, but apparently they can get so big that they can’t eat enough food to keep them alive so they starve to death, if some other animal doesn’t kill them first.
Apparently medical research is being done on them because of this property, with the idea that we could apply it to humans. The immortality part, that is.