I started my menses when I was in the fifth or sixth grade of elementary school; that was between the age of nine to thirteen. I did not know back then whether or not I had to fast. Was I guilty? What can I do to correct this now?
Let me also suppose that I used to fast back in the days, but I am not sure whether or not I made up for the days of fasting that I missed because of my menses given that I was ignorant about the obligation of making up for those days. When I asked my mother about this, she said she could not remember either. What should I do? If I have to make up for the days that I missed, how many days should I fast then, given the fact that I do not remember the exact number? Is it necessary to fast those days before the next Ramadan comes?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and messenger.

A girl reaches the age of puberty if she comes to have menses at the age of nine or above, in which case she becomes legally binding to follow Islamic rulings such as the prayer and fasting. That being said, you are required to make up for the days of fasting that you failed to fast in Ramadan as well as for the days that you missed because of menses. If you cannot remember the exact number of days that you missed, then you are just required to do your best in remembering this. Allaah does not burden a soul with that which goes beyond its capacity. You have got to be careful in your calculations and fast as many days as you mostly think you missed so that you become sure that you have cleared yourself from your liability. We ask Allaah, the Exalted, to guide you to that which He is pleased with.

As long as you were ignorant about the prohibition of delaying fasting the missed days until the following Ramadans came over, you are not required to pay expiations for such delays. In Tuhfat Al-Muhtaaj, Ibn Hajar Al-Haytami quoted Al-Athru‘i as saying:

"If a person delays it (i.e. the fasting of the days that the person missed in Ramadan) out of forgetfulness or ignorance, then there is no expiation on him, as understood from the statements of Muslim scholars. What is meant here is the person’s ignorance about the prohibition of the delay, even if the person is connected with knowledgeable people, since he was unaware of it."

Now, since you have come to know of the obligation of making up for the days that you missed, you have to start right away. Now, you do know that any delays are prohibited and that if you keep delaying this without a valid excuse, you then will have to pay an expiation per day of fasting that you missed. The expiation is to feed a poor person per day.

Allaah Knows best.