On average, most girls start their periods when they're 12 or 13 years old (although some begin earlier or later).
The start of menstruation is a momentous event in a girl's life. Some girls greet those first drops of blood with joy or relief, while others feel bewildered and shy. Whatever the reaction, the arrival of the first period holds the same meaning for every girl: It's proof that she's becoming a woman.
In the early 1900s, girls generally reached menarche (the medical term for the first period or the beginning of menstruation) at age 14 or 15. For a variety of reasons, including better nutrition, girls now usually start to menstruate between the ages of 9 and 16. But menstruation isn't just about having a period. It's a sign that a girl is physically capable of becoming pregnant.
During the menstrual cycle, hormones are released from different parts of the body to help control and prepare the body for pregnancy. That preparation begins when the ovaries (two oval-shaped organs that lie to the upper right and left of the uterus, or womb) produce the hormones estrogen and progesterone.
So people who say it was wrong for the Prophet Muhammad (PBUH) to marry Aisha say that based on the society norms today. But BIOLOGICALLY it is a perfectly normal thing.
Also, the society at the time of the prophet was open to this concept.
We find it wrong, because our society says so. But SCIENCE says other wise.
