1,453. Not Marrying a Minor; Sources for Marriage Methods
Hilchos Ishus 3:19
It is a mitzvah for a man to a marry a woman himself rather than through an agent; it is likewise a mitzvah for a woman to accept the kiddushin herself rather than through an agent. While a father has the power to marry off his minor daughter to anyone he wants, it is not appropriate for one to do so. The Sages enacted that a man should not marry off his daughter until she is old enough to consent. Similarly, it is not appropriate for a man to betroth a minor, nor should he betroth a woman until he sees her first. This is to avoid him not finding her pleasing, with the result that he will divorce her or have relations with her even though he dislikes her.
Hilchos Ishus 3:20
Marriage effected by intimate relations is effective under Biblical law; the same is true of marriage effected by a document. Just as a document can dissolve marriage, as per Deuteronomy 24:1, “He shall write her a bill of divorce,” a document can also effect marriage. Effecting marriage through a monetary transaction is derived from the Torah through rabbinic exegesis. Deuteronomy 24:1 say, “When a man acquires a wife….” The Sages explained that “acquisition” involves a financial transaction, as we see from Genesis 23:13, in which Avraham “acquired” a field through a financial transaction.