A boy attains majority (becomes baligh for adult) when he...
A boy attains majority (becomes baligh for adult) when he reaches the age of fifteen years, or semen is ejaculated from him (in sleep or when he is awake), or pubic hair starts to grow. A girl attains majority when she is nine years old, or when pubic hair starts to grow. When a boy or girl attains majority and is sane (i.e. not mad), he or she is called mukallaf (feminine = mukallafah).
We may translate this term as, one who is obligated to follow the rules of sharia; one who is considered responsible for his/her words and deeds. As soon as one becomes mukallaf, one is responsible for one's belief, words and actions. Before that, generally speaking, one is really neither a believer nor a disbeliever. But a Muslim's child is considered Muslim, and a non-Muslim's child is considered non-Muslim.
It is based on the principle of taba'iyat (following), by which children are governed by the rules that govern their parents. [^1] It is incumbent on every person to have correct faith the moment he or she becomes baligh. Therefore, for all practical purposes, he/she must acquire correct knowledge of fundamental beliefs - Usul al-deen, roots of religion - long before the expected time of attaining bulugh (= majority, adulthood).
There are SEVEN things which the mukallaf must look into at the moment of his/her attaining majority: Roots of Religion, Usul al-deen Learning Salaat (practical, if not learned earlier) If he or she had done anything, during childhood, which makes a ghusl compulsory (e.g.
had touched a dead body), he or she must do ghusl at once in order that his/her salat and other such actions may be correct Learning important rules of salat and other obligatory things like fast, etc (if not learned earlier) If there are other people's right due on him or her, they must be repaid to those persons, or they should be requested to forgive him/her He/she must learn necessary rule of shari'ah regarding his/her occupation or profession, (like trade, partnership, employment, rent etc.), in order that his/ her earnings may be lawful He/she must know the major sins, in order to avoid them; also other unlawful things, so that he/she may protect him or herself from them.[^2] The same rules apply to the one who accepts Islam after spending some time, in kufr.
For a logical explanation of the Roots of Religion, the reader may study my booklet "Islam".[^3] But a short description of its most essential aspects is given here. It will be followed by a list of the major sins.