Nobody would have an issue with some random warring desert nomad having sex with a child 1500 years ago as it was definitely commonplace if it weren't for the fact he's upheld as a revered figure within the Islamic doctrine as the perfect man until the end times who acted in accordance to the will of God.

At that point, the discussion of whether it was commonplace historically is an irrelevance as the claim spans all time - this is where the issue arises. We've advanced as a society and culture to come to the conclusion that children ought not to be subject to adults having sex with them due to the physical impact it can have (which can be very, very severe and the human body hasn't changed enough for this to have been a non-issue even 20,000 years ago) and the logical understanding that children can not consent nor understand the process and is inherently abusive and predatory. To uphold the actions of a man who is capable of such acts and make them a central figure of your theology is to in some way, excuse or justify these actions. He can't have been a product of his time and that part should be ignored and the perfect man for all time, it's one or the other and by todays standards he would be a child rapist.

To your original question, the overwhelming consensus based on texts and accepted in the majority of sects is that Aisha and Muhammad married when she was 6 and consummation happened 3 years later when she was 9 years old. The recent uptick in people trying to change her age has arisen solely because of the criticism and standards we hold today and is considered heresy by mainstream Islam.