Continued Spoilers: I was also confused that Saito was so aged and Cobb wasn't but I just figured it was because time moves more quickly for each lower level. Saito went into limbo first and maybe enough time elapsed in that limbo for him to age. If Cobb knew where to find him relatively quickly then he wouldn't have aged as much. I have no idea if that makes any sense. I really liked Inception and that it was complicated. I appreciated that they didn't dumb the movie down. And the acting was great from everyone but especially Cotillard.
Oh, and I almost forgot to mention...I'm the good cop, he's the bad cop.