Well, as far as i know the hadith about the age of nine comes from bukhari and muslim and i think others. Its one of these subjects you don't hear about. I always thought she was 12 or 13, but bukhari has 3 hadith that says she was 6 when married, and 9 when she moved in. The thing is, you should get a girl's permission before marrying, and i did not see anywhere where aisha was asked about it and plus being 6 its hard to see how she can understand what marriage is.

There is also a hadith by bukhari where aisha was playing with toys with other girls when she married the prophet. So this is obviously a child.