Must I fast three days now, given that I swore by the Qur’an falsely four times when I was 13 years old?

If you swore falsely on the Mushaf while you were not an adult, there is no sin upon you and no expiation; because the oath of a child is not binding. However, if you were an adult at the time of the oath, you have committed a great sin, and you must repent and seek forgiveness. There is no expiation required of you according to most scholars, because what you did is too great for expiation to apply to it. If you swore four times on the Mushaf that you would not lie, and then you lied while being an adult, you are required to pay one expiation for an oath. The expiation for an oath is to feed ten poor people, or clothe them, or free a slave; if you cannot find these, then you must fast for three days.