Menstruation is the shedding of the lining of the uterus (endometrium) accompanied by bleeding. It occurs in approximately monthly cycles except during pregnancy and after menopause. Menstruation marks the reproductive years of a woman's life, from the start of menstruation (menarche) during puberty until its cessation (menopause)
Read what it says..."Menstruation marks the reproductive years of a woman's life"...The prophet had sexual relationship with his Wife Aisha only after the start of her menstruation cycle.
In today's society we may not agree with this...But why does the menstruation cycle start this early ? Have you ever thought about this ? Society accepts and rejects what is in its interest. It will legalize prostitution, gambling etc...
Muslims should not be defensive with regards to the Prophet and his marriage with Aisha...Biologically it is perfectly fine...