Bar Mitzvah is from the Hebrew, literally meaning SON OF COMMANDMENT.Bar Mitzvah means UNDER OBLIGATION (to observe the law) (Alcalay, R. The Complete Hebrew English Dictionary.
At the age of 13 one becomes subject to the commandments (Avot 5:21).
When a vow is made by someone age 13 or above, it is a valid vow (JT Yerushalmi Niddah
Talmud teaches that when one comes of age one must fast on Yom Kippur. This obligation is required only of adults (Ketubah
It is not necessary to have a Bar Mitzvah celebration to BE a Bar Mitzvah. The obligations and responsibilities become a man's when he reaches 13 with or without a formal ceremony. Megilla
Bat Mitzvah is the time when a boy passes to manhood in the eyes of the community. He is thus allowed to participate in various rituals associated with full membership in the community such as ALIYAH - being called to recite the blessing over the Torah; laying tefillin - worn every weekday morning during services; being counted as one to make up a Minyan - the quorum necessary for community prayer.
The Hebrew Letters featured in this piece are Beit Resh - BAR; and Mem Tsade Vav Hey - MITZVAH.