I am leaning towards Fable II opposed to Fable III due to hearing a lot of people are unhappy with Fable III.
But before I make my decision I need to ask a few questions.
 
1. Do you age ridiculously fast like the first one? (I played the Lost Chapters on the PC)
2. How much bigger is the world in 2 and 3 than the first game?
3. Which game do you suggest I buy?

Don't be put off by the Fable 3 hate. I much preferred it to Fable 2, but both suck compared to the mighty original.

I'm not seeing much aging in F2/3, not as noticeable as the first one at least. 
 
From what I remember from 1 the world in 2 is a little bigger, feels bigger anyway and is more fun to banter around in, 3 is pretty large but not many areas you'd revisit after you went through or got the silver keys/etc (bandit camps and the like), the towns are ace and very different in culture/setting/etc.
 
If you can get Fable 2 cheap, might as well, its still a good fun game if you like the series, and then buy 3 after (which is already down to 30 bucks over here) and you'll have your Fable fix for the coming while.

I would say avoid getting any of them.  Fable 2 is better in my opinion but that doesn't mean much.  You do age ridiculously fast in the second one and you don't age at all in the third.