Bar Mitzvah is a "coming off age" Jewish ritual, when a boy turns 13 years old. Bar Mitzvah is an initiation ceremony which introduces young Jewish males into maturity and following the teachings of Torah. Bar Mitzvah signifies the beginning of religious responsibility for a Jewish boy. Bar Mitzvah literally translates into "an (agent) subject to the law."
When a Jewish boy turns 13, he becomes accountable for his actions as per Bar Mitzvah. Until the age of 13, the parents of the boy take the responsibility for his actions. Thus, as per Jewish tradition 13 is the age when the child gains maturity and the wisdom to choose between the right and the wrong and to take mature as well as wise decisions. This is why Bar Mitzvah is called as "coming off age" ritual. Similar to the Bar Mitzvah, when a Jewish girl turns 12, Bat Mitzvah is performed to indicate her coming of age.