Catechism of the Catholic Church §1308 — excerpt
Although Confirmation is sometimes called the "sacrament of Christian maturity," we must not confuse adult faith with the adult age of natural growth, nor forget that the baptismal grace is a grace of free, unmerited election and does not need "ratification" to become effective.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: St. Thomas Aquinas, STh III, 72, 8, ad 2