Muhammad didn’t marry her at 9. It was fabricated later by narrators to praise Aisha.
Ibn Ishaq (earliest source) reports that Aisha converted to Islam in first 3 years (610-613) of mission
Aisha must be at least 5 years old in 613. Marriage occurs in 623 when she is age 15

@pearlythingz if you’re going to go based on accepting Sunni Muslim sources, the same sources tell us Aisha was not prepubescent when the marriage occurred. At best the sources contradict each other and the earliest Muslim sources negate her being 9 at marriage

One can also dispute and reject the story from a Sunni traditionalist point of view.
I’ve seen at least 3 Sunni scholars who respect their tradition offer alternatives by using a source l critical approach to their corpus of writings m.

Ibn Ishaq himself didn’t record or narrate the story that Aisha was 9 at marriage. It’s Ibn Hisham who adds this to the story in his edition.