18
It is 12.
Menstruation
Ovulation does occur before menarche. Menarche is the term used to describe a girls first period, menstruation will only occur if the woman ovulates. With that said some people will experience vaginal bleeding as a result of hormonal imbalance which will look like menstruation but without ovulation occurring beforehand, and sometimes we call that menarche - because we've no way of knowing if ovulation had occurred.
The average age of menarche (first period) is 13 years old, however anything between 10-16 is considered normal. In rare cases girls can start menstruation far earlier, the worlds youngest ever recorded mother for example reached menarche at just 2 years old.
Well, the menstruation starts at the age of 12-13 in girls. The term for onset of menstruation is menarche .
I am going to assume that by this you mean menstruation - where the lining of the uterus is shed and exists the body via the vagina. Typically girls reach menarche (first period/menstruation) around the age of 13 years old, a few years into puberty, but everyone is different. Anywhere between 10-16 years old is considered within normal range for starting menarche, if a girl is over 16 years old and has yet to start menstruating she should see her doctor.
Females are born with all the eggs they will ever have. The process of producing eggs begins before birth, with a female baby born with around 1-2 million eggs in her ovaries. However, these eggs are not fully matured until puberty.
The term menarche means beginning of menstruation in girls. The usual age of this is 12 years.
The average age for menarche for girls is under 13 years of age. However, individually speaking that can vary depending on several factors including weight.
Girls can become pregnant as soon as they start puberty, which usually occurs between the ages of 10 and 14. However, the average age for girls to become pregnant varies depending on factors such as access to education, healthcare, and contraception.
Menarche is the first menstrual flow onset of puberty in girls while menopause is the time when ovaries of a woman stop releasing eggs.
The first menstruation can be as young as 9. In the US the average age for girls to start menstruating is 12.