RWS

1) From the order of events near the end of the movie, Mal kills Fischer, then Cobb and Ariadne decide to go down into limbo after him. They go to sleep and wake up in limbo. A couple minutes later on the third level, Saito dies. Cobb correctly guesses that Saito will die before they are able to ride the kick back to reality, and so decides to stay in limbo and search for Saito. We then find Cobb on the shore of limbo and is brought to see Saito, who is now an old man. Cobb, however, is still young. But how is Cobb still young when he entered limbo before Saito did, and stayed the entire time to search for him? Shouldn't he be older than Saito?

2) In order to get down to limbo, Cobb and Ariadne simply go to sleep again - they don't kill themselves. Does this mean that limbo is only 4 levels deep? Also, how come they remember where they came from when they enter limbo, but both Saito and Cobb and Mal forgot about reality when they entered limbo?