I know there was one episode in which Clark tells Lois he simply ages slower than a normal human being.
Mona, I'm not sure which episode you're thinking of but I wonder if you mean Brutal Youth? It's the only episode that deals with the aging issue, I believe.
But Lois gets the idea from Dr. Klein, not Clark - it's Klein's hypothesis and so he has no way of knowing for sure whether he's right although Klein is always enthusiastic about any of his ideas.
(that's what research scientists get paid for <g>) Nor can Klein know how long term exposure to the earth's environment will affect Clark.
In BY, it's Lois who tells Clark about Klein's comment.
Needless to say though, Lois was freaked out by the idea and had these horrible visions and nightmares of her future with Clark. (as you can imagine - this is every woman's nightmare : that she will look older than her husband. North America has developed a thriving cosmetics and plastic surgery industry exploiting this anti-aging fear.)
But by the end of Brutal Youth, Clark had transferred some of his "life" force to Jimmy and so we're left not knowing exactly how long Clark might have. What if he'd traded off so much of his life force that he had only a few years left? Or what if Klein's hypothesis was wrong in the first place? Or what if Clark begins to suffer from Earths' environment? (Yvonne Connell wrote an excellent fanfic on this latter idea - Heliophobia)
c.
