Let me be blunt as explained to me by a Muslim. The fact that Mohammed was an old man and could maintain an erection sufficient to deflower a 9 year-old is impressive to Muslim men. I'll be surprised if they didn't fly the sheets from the flagpole.
The fact that Mohammed was an old man and could maintain an erection sufficient to deflower a 9 year-old is impressive to Muslim men. A structural thing, IOW -- the shaft did not buckle when subjected to a certain axial stress.
And I'll be blunt right back at you: it suggests to me that my initial take was correct -- he couldn't force his old man's erection into the very small vagina of a 6-yo girl, and thus had to wait until she (and her vagina) got larger.