that's what I found...
Many people mock the idea that a 12 or 13 year old child is an adult, claiming that it is an outdated notion based on the needs of an agricultural society.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.