You are refering to Aisha. She is not part of cannon musslim tradition (as in she isnt in the quran).
The age of her, if she had sex, and when are all debated points and not clearly identified int he Quran.
This rumor is about the same as the rumor around Mary being a prostitute... its speculation at best.
A Jihad is a difficult personal battle with some spirtual reward.. for example the proper word for a musslim getting over a drug addiction or overcoming some other struggle and finding spirtual growth from it would be called a Jihad.
How is any of that against christianity... it sounds like you were just really REALLY misinformed.