פירוש על קידושין 58:19

Here we can get a sense of why the rabbis urge men (boys) to marry so early—to ward off “Satan.” This is probably a way of expressing the sexual urge. Unmarried boys over the age of puberty will almost certainly either masturbate or engage in illicit sex, both activities the rabbis did not condone. To prevent this, it would be best to marry as young as 14. But again, this does not mean that people actually did so.