Reaching the age of majority was not always a requirement for commandments such as being called up to the Torah.
How Old is Old Enough?
Contemporary Bar/Bat Mitzvah Issues. The Bar / Bat Mitzvah Celebrarion. Jewish Coming of Age. Jewish Lifecycle
The bar mitzvah (and even more so the bat mitzvah) is a relatively new phenomena.
Age and its significance, terminology, parents' blessing, parent-child dynamics, and motivations for adult bar/bat mitzvah.