>Ideally it would show that the Quereysh copied the Jewish practice while lowering the minimum age for marriage from 12 to 9 and fro betrothal from 3 to 0..
That's kinda hard. Muslim wipe out all the litterature in pre-Islam age. Try these:
The History of Al-Tabari, Vol. 6: Muhammad at Mecca
The Life Of Muhammad, by Ibn Ishaq
The Meaning of the Qur'an vol 1 - Sayyid Abul Ala Maududi