"If we look at the issue taking 614 as the year that Surah Qamar was revealed, Aisha would have been born at least eight years before the prophetic mission, or in 606. If we accept 618, then the year of birth would have been 610; this event alone makes it impossible for her to have been 9 when she married."
complete link:
http://www.islamicity.com/articles/articles.asp?ref=ic0811-3718