Tertullian, On Baptism 18

People whose job it is know that Baptism must not be accepted rashly. You hand your own to every petitioner, and that gift carries a title that counts just the same as almsgiving. Rather, you must grasp this: do not give holy things to dogs, and do not cast your pearls before swine, and do not impose hands easily, lest you become partners in strangers' sins (Matthew 7:6). If Philip baptized the eunuch so easily, consider that the Lord's manifest and evident dignity intervened. The Spirit had ordered Philip to take that road; the eunuch was found neither idle nor suddenly craving baptism, but he had gone to the temple to pray, impressed by divine Scripture. So it had to happen that the man to whom God sent an Apostle on his own initiative was seized; the Spirit then commanded Philip to join the eunuch's chariot, the Scripture of his faith turned up at the right moment, he was exhorted and taken up, the Lord was revealed, faith did not wait, water was not delayed, and the Apostle was snatched away with the task finished. Paul, too, was baptized quickly. He had quickly recognized that his host Simon was a vessel of election constituted by God. The dignity of God sends out its own prerogatives; every petition can both deceive and be deceived. Therefore, according to the condition and disposition of each person — even their age — delaying Baptism is more useful, especially with young children. Why impose danger on sponsors as well? They themselves can fail their promises through death, and be deceived by the outcome of a bad character. The Lord says: Do not prohibit them from coming to me (Matthew 19:14). So let them come while they grow up, let them come while they learn, while they are taught where they are coming; let them become Christians when they can know Christ. Why does innocent age rush to the remission of sins? One acts more cautiously in worldly matters, so that to whom earthly substance is not entrusted, divine substance may be entrusted; let them know how to seek salvation, so that you may seem to have given to the one who asks. For no lesser reason the unmarried are also to be delayed, in whom temptation lies ready both for virgins through maturity and for widows through wandering, until they either marry or are strengthened in continence. If anyone understands the weight of Baptism, they will fear the consequence more than the delay: intact faith is secure concerning salvation.