Thank you for your question.
There are two views on the matter.
The view that Aisha was 9 when she married the Prophet (saw) is based on a narration in which she states her age at the time.
However, based on the claim that she was one of the first believers in the prophetic mission it seems that she would have had to be in her teens and at that probably her late teens when she married the Prophet (saw). Proponents of this view also mention that it was likely that Aisha was understating her age to appear younger.
A scholar that holds the second view is Sayyid Jafar Murtada al-Amili, and it is not an uncommon view.
May you always be successful