In most cases, a person becomes capable of understanding and keeping Gods commands at puberty (age 13-14) for most.
The Jews have a coming of age celebration then called bar/bat mitzvah.
Is 13 an Adult?
Many people mock the idea that a 12 or 13 year old child is an adult, claiming that it is an outdated notion based on the needs of an agricultural society. This criticism comes from a misunderstanding of the significance of becoming a bar mitzvah.
Bar mitzvah is not about being a full adult in every sense of the word, ready to marry, go out on your own, earn a living and raise children. The Talmud makes this abundantly clear. In Pirkei Avot, it is said that while 13 is the proper age for fulfillment of the Commandments, 18 is the proper age for marriage and 20 is the proper age for earning a livelihood. Elsewhere in the Talmud, the proper age for marriage is said to be 16-24.
Bar mitzvah is simply the age when a person is held responsible for his actions and minimally qualified to marry. If you compare this to secular law, you will find that it is not so very far from our modern notions of a child's maturity. In Anglo-American common law, a child of the age of 14 is old enough to assume many of the responsibilities of an adult, including minimal criminal liability. Under United States law, 14 is the minimum age of employment for most occupations (though working hours are limited so as not to interfere with school). In many states, a fourteen year old can marry with parental consent. Children of any age are permitted to testify in court, and children over the age of 14 are permitted to have significant input into custody decisions in cases of divorce. Certainly, a 13-year-old child is capable of knowing the difference between right and wrong and of being held responsible for his actions, and that is all it really means to become a bar mitzvah.