The Christian ceremony that confirms a baptized person’s faith and is commonly treated as a coming-of-age milestone is Confirmation.
Confirmation is a sacrament or rite in many Christian traditions. In Catholic, Eastern Orthodox, Anglican, and several Protestant communities, it is associated with strengthening or affirming baptismal faith and receiving a fuller responsibility within the church. The exact theology, age, and ceremony differ by denomination.
Some churches confirm children, while others confirm teenagers or adults after a period of instruction. That variation is why Confirmation is not tied to one universal birthday. In many families it still functions socially as a coming-of-age event, even where the church describes it primarily as a religious sacrament.
Confirmation is distinct from baptism, which initiates a person into the Christian community, and from first Communion, which concerns receiving the Eucharist. The three may occur at different ages and in different sequences.