I liked it all except for the ending. I saw it coming, and I didn't like the ambiguousness of it.

I think the vagueness of the ending is what made it even more brilliant. It was as vague as the dream world they were in. The paradox is that if the top eventually stops spinning, we know he's in the real world, but we can never find that out for certain.

the entire movie was a dream.

Think about how old Saito was just before he and Dom kicked out of Limbo and back to the plane. How did he come to be so old while Dom was so young, considering that he was still alive when Dom and Ariadne went to Limbo to rescue Fischer. That's either an inconsistency or requires some tricky explaining.

Think about how old Saito was just before he and Dom kicked out of Limbo and back to the plane. How did he come to be so old while Dom was so young, considering that he was still alive when Dom and Ariadne went to Limbo to rescue Fischer. That's either an inconsistency or requires some tricky explaining.

I believe Saito has been dead for several minutes before Cobb and Ariadne make the jump into limbo. As the movie demonstrates, time changes exponentially depending on the level of dream. I am unsure if 5-10 minutes passing in level 3 (ice fortress) is 50 years in limbo for old Saito; but, it could be a viable explanation.

We know from the Cobb and Mal storyline that they “grew old together in limbo”. They killed themselves with the train after spending decades in limbo. They awoke to be young adults again; so we can conclude that a lifetime in limbo is a relatively short amount of time in the real world.

The truth is we never see what happens to Cobb between emotionally letting go of Mal in the crumbling limbo and arriving on the beach of Saito’s place. All we know is that Cobb is still fairly young and Saito is rather old. After the first screening, everyone I went to the movie with assumed it was because Cobb entered limbo at a later time than Saito.

We are debating dream levels, time disparities, and subconscious renderings of people in a movie. Nevertheless, I felt it stayed within its logical framework. A lot of it is open to interpretation (For example, the cutoff of the spinning top at the end was timed perfectly to create a state of uncertainty. The movie ended with the spinning top bobbling and possibly beginning to waiver. If it would have ended without a bobble people would have concluded he was dreaming, and if it would have ended with it toppling people would have known it was real life. Either way he was happy, why does it necessary matter if he was dreaming or not?)

While it is possible, I see no proof the ending scene was a dream.

his kids looked the same throughout the entire movie? even their clothes and how they were playing. If it was the real world at the end, wouldn't they be a few years older?

Can you explain why...
his kids looked the same throughout the entire movie? even their clothes and how they were playing. If it was the real world at the end, wouldn't they be a few years older?

From IMDB casting:
http://www.imdb.com/title/tt1375666/fullcredits#cast

Claire Geare ... Phillipa (3 years)
Magnus Nolan ... James (20 months)

Taylor Geare ... Phillipa (5 years)
Johnathan Geare ... James (3 years)

Kids look similar, but played by different actors. As far as clothing, I have heard some arguments that while the garments look similar, they are in fact slightly different. I haven’t seen any screenshots to confirm or deny this claim, and my memory isn’t near that detailed to remember.

In addition, we are never given a time frame from Mal’s suicide until the movies events (for all we know it could be 6 months).

From his urgency and the grandpa's responses, I was assuming it had been at least a couple years.

The only aspect of your explanation that I can't find myself in immediate agreement with is that Saito was dead before Dom and Ariadne went into Limbo. In particular, I recall Dom saying to Ariadne something like "Saito is dead by now, which means he's down here. I've gotta find him and give him the kick". If I'm misremembering, and Saito did in fact die some minutes before Dom and Ariadne dropped into Limbo, then that explains the age discrepancy. A different explanation is presented in the wiki article which suggests that Dom dies of the stab wound and loops back into limbo because he's still under the effects of the sedative, and that this death/return cycle somehow gives Saito time to age. Of course, the wiki article also states that Saito died before Mal shot Fischer, which I am relatively certain is not how events occurred (Saito died after firing shots and throwing a grenade into the ventilation shaft to delay the agents of Fischer's subconscious - while Fischer was laying dead on the floor, awaiting the kick from Limbo), so take the article's recounting with a grain of salt.