In the East this sacrament is administered immediately after Baptism and is followed by participation in the Eucharist; this tradition highlights the unity of the three sacraments of Christian initiation. In the Latin Church this sacrament is administered when the age of reason has been reached, and its celebration is ordinarily reserved to the bishop, thus signifying that this sacrament strengthens the ecclesial bond.
Source: Catechism of the Catholic Church (Vatican.va)