פירוש על קידושין 7:3

This other midrash is more directly related to the verses of the Torah. The Torah specifies that a girl bought as a slave at a young age “goes out” if the master does not do certain things on her behalf (like marry her, or marry her off to his son). But there would seem to be the need for a time-limit. The rabbis invent such a time limit, and apply it here and elsewhere. A “ketanah” is a girl under 12. A girl between 12 and 12 ½ is called a “na’arah” and after that she becomes a “bogeret.” This midrash teaches that if the master has not done these things before she hits 12, she goes out free and need not pay any money for her manumission.