In Inception, I don't understand the ending where Cobb and Saito find themselves independently in limbo. Is it a coincidence that Cobb found Saito in limbo and that too just before the plane flight in the real-world arrives at its destination?
No coincidence; remember, the Realworld / Dreamworld time ratio keeps getting more and more severe as you go deeper and deeper. The amount of time he had to search in Limbo was tremendous; it would equate to a very short time in RL, so it being completed before the plane landed is no real surprise.
Saito found Cobb. Or rather his men (projections) found Cobb. On the beach, where one arrive when entering limbo.
I think Cobb caught the kick out into the snow world and then re-entered limbo (possibly by dying in the exploding building). This explains why Cobb is young and Saito is old.
Saito had lived in limbo for a long time and monitored the beach, in case someone else came to limbo.