Or then Flint did the Ardra thing and merely put smoke and mirrors between the planetside heroes and their ship. In both "Devil's Due" and this ep, the camera shows the orbiting ship disappearing "for real" - but in the TNG episode, this is only because the ship is hidden behind a cloak. The same might be true here.
I think this is something you would outgrow in 7,000 years. Our grandparents lived in a world where a single generation had a single type of environment around them. Their great-grandparents lived in one where a hundred generations could go without needing to confront a change. But our parents are living through major changes every decade, and surviving. Annual change might be the near-future norm, and generations would emerge that can cope despite having been born sixteen or thirty cycles earlier.
Flint's lifespan would expose him to the dozens-of-upheavals-per-generation pace simply through the generation being so darn long; he would in essence have experienced the 2010s back in 400 BC-through-AD 1200 already.
Timo Saloniemi
Also, Flint is not just any immortal--he is a supergenius. His accomplishments didn't simply flow from age, if he was all those others. He was da Vinci, after all.
But although we might retroactively explain the Enterprise disappearing as a cloak, I really don't think that was what was intended Timo. I think we were supposed to say, "he shrank the whole friggin' Enterprise and put it on his dining room table!" Because Kirk sees (and we see) the bridge crew through the front of the model (what this says about the viewscreen, I don't know. Best to ignore that aspect, probably.)
And I'm inclined to believe his whole story, because McCoy confirms from "correlated"-with- earth-records tricorder readings that he (Flint) is aging on this planet and will die of old age. This suggests to me that McCoy was able to verify that some weird field effect of earth--as he explains--on Flint's biology was what kept him undying. Meaning that Flint's story IS verified, or as definitively as the Enterprise, Federation science, and Bones were capable of verifying it, which I think we have to settle for. By season 3 McCoy is a pretty wide/deep-thinking xenobiologist.
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"The joys of love made her human, and the agonies of love destroyed her."
Spock's line about the joys and agonies of love was pretty out of charatcer for him, but in the staging of a
play, was perfect--the outsider narrates the truth for all of us. For that reason I don't care how odd a comment it is for a Vulcan, it's beautiful, classic direction. And we might also argue, continuity-wise, that Spock was forever changed by the spores and the impact of the events in This Side of Paradise. I'd like to believe that. And the mind-melds he has done (Horta, NOMAD) are probably more than a little atypical, too, and might have altered him to some degree. But mostly I think Leila and the spores would have had the most lasting impacts, because Vulcans would have deveoped mechanisms for coping with mind-meld feedback issues.