Where did Bar and Bat Mitzvah come from?

I found this in a book called Living a Jewish Life that helps me from time to time:

"Bar mitzvah does not appear in the bible, which gives the age of 20 as the time when adult obligations begin. However, by the first century CD adulthood was universally held to begin at 13 for boys and 12 for girls, a view codified in the Talmud, which states, "At age 13, one becomes subject to the commandments." The earliest reference to any ceremony to mark this change dates from the Second Temple period, when a special blessing was recited for 13-year-old boys who had completed their first Yom Kippur fast. But until the Middle Ages, the religious distinction between a 10-year-old and a 13-year-old was strictly theoretical. Children were regularly counted for the purposes of creating a minyan, the quorum often needed for certain prayers, so that reaching the age of 13 was not associated with any particular rituals or celebrations.

That approach to ritual maturity changed drastically sometime between the 14 and 16th century in Germany and Poland, where minors were no longer permitted to read from the Torah or be counted in a minyan. From that point in history, bar mizvah became an important life-cycle event throughout the Jewish world. Boys were called to the Torah to symbolize the attainment of adult status in the prayer life of the community.

The central act of this rite was receiving the honor of an aliyah, of being called to bless and/or read from the Torah. However, other elements were soon added to the ceremony. As early as the 16th century, bar mizvah boys were delivered d'rashot, discourses on the Torah portion that they had read. In the 17th and 18th century, some synagogues permitted accomplished students to lead part of the service as well. As with every joyful occasion, ,or simcha, bar mitzvah carried with it the obligation of a seudat mitzvah, a commanded meal of celebration.

Bat Mitvah

Because girls' coming of age was not connected with the performance of public religious rites, the notion of a parallel synagogue ceremony for girls was unthinkable before the modern era. In some German communities, families would hold a sudah, a party, on the occasion of a daughter's 12th birth day, and although a girl might deliver a speech and her father recite a blessing, this was not a religious ceremony.

Bat mitzvah is a 20th century innovation. Although the Reform movement officially instituted equality between the sexes in the late 19th century, the first recorded bat mitzvah did not occur until 1922. It was celebrated by Judith Kaplan (Eisenstein), the eldest daughter of Mordecai Kaplan, the founder of the Reconstructionist movement. The practice did not become commonplace until the 1950s, first in Reform congregations and then in Conservative synagogues.

For many years, bar and bat mitzvah were distinctly different. Boys were usually expected to read or chant a Torah or haftarah portion on Saturday morning whereas girls were limited to a Friday night reading from the haftarah. The differences between bar and bat mitzvah have been steadily diminishing to the point that today, in many congregations, they are virtually indistinguishable. (Bar and bat mitzvah are, therefore, treated interchangeably in this chapter of the book LIVING A JEWISH LIFE: Jewish Traditions, Customs and Values for Today's Families by Anita Diamant and Howard Cooper p. 254-255.)

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