Actually - I didn't say he was immortal, although - since the legend of Superman (and Lois) is revered through time, by my dictionary definition (Collins) Clark/Superman (and Lois) could technically be defined as such.
I was implying Clark has a different set of boundaries on him than Lois. While his mortality can be compromised, it isn't as earthly in distinction as Lois's because of the simple fact he is invulnerable to most situations unless kryptonite is used. I wasn't even thinking of the whole 'live forever' situation which really has too many variables in the show (as you mentioned) to allow us to know conclusively what the effects of exposure to various situations have caused to Clark's original potential/theoretical lifespan. I guess that is a gift to fanfic writers because it does offer so many wide and varying scenarios for them to explore while still staying true to the realms of the Lois and Clark genre.
