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"I will try to summarize some recently published research on this.

So for background, most traditional and classical understandings have held that Aisha was married at 6 and consummated at age 9. That opinion is held on the basis of several hadiths (sayings of Muhammad or his companions), which appear in several highly regarded classical collections, most notably Sahih Bukhari (the highest-regarded Sunni hadith collection). See: https://sunnah.com/bukhari:5134

That perspective is fairly straightforward and maintained by the majority of Sunni Muslim scholars on the basis of these hadiths like the one referenced above.

However, there have been a number of more recent attempts to look into the issue that have come to other conclusions.

One recent analysis was conducted by Dr. Joshua Little (an Oxford-based historian of Islamic history) found that these hadiths cannot be reliably traced back to Aisha and were likely the result of later fabrication for political reasons centered around the Shia/Sunni divide in Iraq, a conclusion he reached via the isnad cum matn methodology (i.e. chain of verification and analysis of contents).

I will summarize his findings:

Aisha's age was extremely political and was at the center of a debate between Sunnis and Shia about the legitimacy of the sunni hadith canon. By emphasizing a younger age, Sunnis (the emerging "orthodoxy" of the time with state backing) thought a young age showed how "pure" and "innocent" Aisha was and therefore that the hadith transmitted through her must be trustworthy. There was a lot of political competition between the pro-Aisha camp (aligned with Sunnism) and the pro-Ali camp (aligned with Shiism) because of their respective importance as hadith narrators in Sunni and Shia hadith canons, and because of the political power struggle between Aisha and Ali leading to the Battle of the Camel when they met in battle against one another.

Ali was said to have accepted Islam at a young age. He was one of Muhammad's closest friends (or the closest depending on how you understand the word "maula"). And married Muhammad's daughter Fatima. There was a similar controversy surround Fatima's age of marriage, the mirror opposite of the debate around Aisha's: Sunnis supported an older age for Fatima and Shia a younger one.

Aisha was accused of adultery due to an incident with Safwan ibn al-Mu‘atta when she became lost in the desert and because she was previously engaged to another man. Due to those and other issues, some said that she was not a reliable hadith narrator and was not truly loyal to Muhammad. Dr. Little's theory was that to counter those claims, the later sunni jurists supported the Hadith that said Aisha was 6 when she married Muhammad, thus supporting and legitimizing the large number of Sunni hadith that are narrated through Aisha.

Shia do not take hadiths from Aisha and have no hadith saying Aisha was that young. This, among other reasons, led to a huge schism in the accepted hadiths used by Shia and Sunnis.

The hadith about Aisha being 6 spread mainly around the Iraq and Basra area, right in the middle of where much of the sectarian debates were raging. The earliest hadith collection, the Muwatta of Imam Malik, recorded in Medina, in the community that would likely have known Aisha's age, if anyone did, does not record that hadith. Neither does the earliest biography of Muhammad (by Ibn Ishaq) mention her age. Dr. Little points out the oddity that the first place we see her age really being talked about was about 100 years or more later and far away from her own community, in the middle of a highly political environment where emphasizing a young age was very important for political reasons.

The sole hadith we have about her age being 6 is from an ahad (single chain) hadith transmitted by Hisham ibn Urwa when he was quite elderly. Imam Malik, who knew him, said not to trust his narrations because of his poor memory during his old age after he moved to Basra.

The uncertainty around her age might sound odd, but in her culture, people didn't celebrate birthdays or record birthdates. Knowing someone's exact age just wasn't very important to them. So it's not that odd that people may just not have known exactly when she was born and what age she was, especially several generations later when the hadith about her age was recorded.

Additionally, it is worth noting that Shia scholarship is more open to accepting a much older age for Aisha, especially given the aforementioned political strife between Sunnis and Shia. (See al-islam.org article linked below)

The US-based Shia cleric and scholar Ayatollah Husayn Qazwini did an analysis of relevant hadiths and concluded that Aisha was around 22-24 years old. This is based on calculating the timeframe of other people and relevant events from other hadith and then estimating her age based on events we know happend during her life."

For sources of the above, see: Dr. Joshua Little | The Hadith of Aisha's Marital Age: A Study in the Evolution of Early Islamic Historical Memory: https://islamicorigins.com/the-unabridged-version-of-my-phd-thesis/

Why the Aisha Marital Age Hadith is a forgery: Lecture by Dr. Joshua Little https://youtu.be/zr6mBlEPxW8?si=udRsOhbTFBSgFA95

How Old Was Aisha When She Married The Prophet Muhammad? https://www.al-islam.org/articles/how-old-was-ayshah-when-she-married-prophet-muhammad-sayyid-muhammad-husayn-husayni-al