Inception Explained
This is a very specific post, and admittedly, uber geeky. :) Read on only if you've seen the movie and want to solve its puzzles.
Question 1: Why is Saito so much older than Cobb in limbo?
One theory is that Cobb entered limbo twice. The first time was with Ariadne. They found Fischer and kicked him back to Eames' dream. Meanwhile Saito dies and goes to limbo. Cobb provokes Mal into attacking him. (Note: He provoked her very methodically, a conscious choice he made for some reason, and this theory is one explanation for it.)
Mal dies from Ariadne's gunshot wound and Cobb dies from Mal's knife wound. At this point, Cobb is currently dying in all 3 levels (in 3, crushed by the exploding snow fortress; in 2, in the crashing elevator; in 1, left to drown in the van.) When he dies in limbo, he wakes up in one of (or perhaps all of) these levels and dies again, sending him to limbo and washing up on the shore near Saito's palace. Saito, having been in limbo this whole time, has aged decades while Cobb is just arriving to limbo for the second time.
Source: IMBD
Question 2: How do the characters kick back to real life?
- Reality - Plane
- Level 1 - Van - Yusuf
- Level 2 - Hotel - Arthur
- Level 3 - Arctic - Eames
- Level 4 - Limbo - Saito, Ariadne, Cobb, Fischer
Yusuf - is in level 1, wakes up when the timer goes off in the plane.
Arthur - wakes up from level 2 with the kick when the van hits the water, then wakes up into reality when the timer goes off.
Eames - wakes up from level 3 when the elevator crashes, then wakes up from level 2 when the van hits the water, then wakes up into reality when the timer goes off.
Ariadne and Fischer - wake up from level 4/limbo my killing themselves (jumping off the porch), wake up from level 3 when the elevator crashes, then wake up from level 2 when the van hits the water, then wake up into reality when the timer goes off.
Saito and Cobb - In limbo, Cobb finds Saito, Saito kills Cobb then himself. It's not clear if they go to reality directly when the timer goes off on the airplane (like Mal and Cobb previously in the movie), but that is most likely. If they woke up in level 3, they would have missed the elevator crash to wake them into level 2. They would have also missed the kick from the van in level 1 that is already submerged to escape from level 2.
Source: Reddit
Question 3: Does the top fall???