The need is to understand that what we call Sharia today includes a number of pre-Islamic Arab traditions and customary practices known as aadat (literally practices). Since the Quran was revealed among the Arabs and they were the first to embrace Islam their practices were accepted as part of Sharia law and Islamic principles had to be applied to the body of these aadat. But when Islam spread to other areas local customary laws also continued to be practised.

It is doubtful if the Prophet of Islam would marry such a young child.

The author is stating that Muhammad did not marry Aisha? or that she wasn't a child when he married her?

Modern
researchers have established that the hadith regarding Hazrat Aisha’s
marriage appeared some 300 years after the death of the Holy Prophet.
It cannot be relied upon.

From the clipped source.

The author is arguing about her age, I don't think there is any doubt that Muhammad married Aisha.

Okay, thanks. There is a wealth of information on both sides of this issue.

I agree, I'm not sure if I even agree with the author here but I am more than willing to accept an opposing point of view if there is a space for more research and substance in a long run helping correct age old practice which is wrong.