The good folks at Alley Cat Allies have created a webpage that shows the age progression of kittens - what you can expect at a certain age regarding appearances, nutrition needs, use of a litter box, etc.

The pictures are especially great - you get a very good overview of the age progression and how it appears.

It's a great web page - you are sure to learn a lot from it.

The Petfinder website also has a page about the aging progression of kittens into adulthood. While they note that the page is incomplete (still "under construction") there is nevertheless a lot of good information about this subject here too - check it out!