

It’s an appealing theory, but how would you square it with the end episode reveal that Flint was no longer immortal since having left earth? Was McCoy just wrong when he reported that readings from the earlier tricorder scan show that Flint has been aging normally since he left Earth’s environment, and will soon die? We know little enough about Lanthanites in general, and Pelia in particular but it is implied that they are an alien race, so their long lifespan isn’t likely to be linked to remaining on earth, unlike Flint’s. Perhaps it wasn’t leaving earth that cancelled Flint’s immortality, but some element on Holberg 917-G?
Eh, it’s no more problematic than the many canon retcons we’ve gotten. It may be there was an element on both earth and the Lanthanite homeworld that maintains Lanthanite immortality, but that element was lacking on Flint’s planet.