"The last immortal man" line in Xanadu. Always funny to me.

Ok so I know it's probably a metaphor of some kind, AND that it could be referred to a population akin to the Highlanders or Achilles (immune to all perils but a single one).

Still I've always found it funny, cause if we were to take it literally, "the last immortal man" must also be the only one that's ever existed, cause if other immortal men existed in the past and they are actually immortal, they'd still be there.

Sorry for this random post, but I had to tell someone.