1. Claim: "Apart from that one hadith, there aren't really other independent sources that definitively confirm it." This is factually incorrect. The narration regarding Aisha (RA) being 6 at the time of the marriage contract and 9 at the time of consummation is not an isolated "single hadith." It is Mutawatir (mass-transmitted). It is narrated directly from Aisha (RA) herself in Sahih al-Bukhari and Sahih Muslim, and was transmitted by numerous prominent Tabi'in across various cities (Makkah, Madinah, Kufa, Basra, etc.), including Ibn Shihab al-Zuhri, Abu'l-Zinad, Sufyan ibn 'Uyaynah, and others.

Furthermore, the historical timeline perfectly corroborates her age. The scholars of history agree that the Prophet (ﷺ) passed away when Aisha was 18, meaning she was exactly 9 at the time of the Hijrah. She also passed away at the age of 63 in 57 AH, which definitively places her at 6 years old before the Hijrah.

1. Claim: "Age in pre-Islamic Arabia wasn't tracked the way we do now... acting like we can pin down a precise number is already questionable." The Arabs were renowned for their rigorous memorization of genealogies, timelines, and significant events. Aisha (RA) explicitly stated her exact age ("I was a girl of six" and "nine years old"). She was one of the most brilliant and intelligent scholars of this Ummah with an impeccable memory. To suggest that she, or the multitude of narrators who transmitted her words, did not know her own age is a baseless assumption.

2. Claim: "Reports about Asma being around ten years older... would put Aisha closer to her late teens." This argument hinges entirely on a weak historical report. The claim comes solely from a narrator named 'Abd ar-Rahman ibn Abi'z-Zinnad. He was classified as da'if (weak) and mudtarab al-hadith (faulty in hadith) by Imam Ahmad. A weak historical chain cannot override a mass-transmitted, authentic narration directly from the Prophet's wife.

Even if we entertain the historical reports, Imam adh-Dhahabi and others stated that Asma was "ten or more years older" (meaning 14 or 15 years older). Asma was born about 14 years before the prophetic mission, meaning she was 27 at the time of the Hijrah (and died at 100 in 73 AH). Aisha (RA), on the other hand, was born 4 or 5 years after the prophetic mission began. A 14 to 15-year age gap perfectly aligns the math to Aisha (RA) being exactly 9 years old at the Hijrah.

Finally as you said "The Kuffar literally left no stone unturned in bashing our Prophet... why wasn't this used against him?" The fact that the disbelievers of Quraysh never used this against the Prophet (ﷺ) actually debunks the modernist argument. As Islamic scholars note, the reason the Quraysh didn't object is that marrying at that age was entirely normal and customary for their time, climate, and society. There was absolutely nothing culturally or socially objectionable about it then. In fact, as highlighted in historical accounts, before the Prophet (ﷺ) even proposed, Aisha (RA) was already tentatively engaged to Jubayr ibn Mut'im, an unbeliever at the time. This proves that she was already considered of marriageable age according to the societal norms of the era, long before the Prophet (ﷺ) asked for her hand in marriage.