So we know that Nirn humans can live only about as long as real humans and that elves can live ~1000 years before keeling over. So how long does it take for an Argonian or a Khajiit to grow old and die? Does anybody have any sources on this?

Argonians, one could reasonably assume, live as long as the Hist wants them to.

As for the Khajit one has to account for possible differences in lifespan for the different forms.

Do we account for each for each of the Khajiit's nine lives ?

Cat jokes

Well, based on what I know from RPGs, the D&D 3.5e catfolk have the same lifespan as a human. That being said, since the first Khajiit were transformed by Azurah from Bosmer, it would be reasonable to say that Khajiit have longer lifespans than the races of man, possibly even the same length as elves (I hope). But considering the Khajiit culture around the Sugar, it could be shortened by the drug, but there is no way to know for sure whether this is true. Different Khajiit morphology might also play a role, but as far as I know, this is probably not a factor.