In Jewish tradition, a boy reaches the age of adult religious obligation at thirteen, which includes responsibility for the Yom Kippur fast when health permits.
This age is closely connected with bar mitzvah. The ceremony may be held on or after a boy’s thirteenth Hebrew birthday, but the underlying religious status comes from reaching the age established in Jewish law and tradition. The date is therefore calculated using the Hebrew calendar rather than simply counting from a Gregorian birthday.
Fasting rules are subject to important exceptions. Jewish law generally requires protecting health, and children, pregnant people, nursing parents, and people with medical conditions may have different obligations or may be instructed not to fast. A qualified rabbi and medical professional can provide guidance in an individual case.
The number thirteen is distinct from the age often associated with bat mitzvah. In many traditional communities, girls reach this status at twelve, while some liberal communities use different ceremonial practices or emphasize equal public milestones.