פירוש על קידושין 37:6

Rav Ashi provides an entirely different context to the baraita. The minor here is a minor yavam (brother-in-law) who is nine years old. This is the age from which the rabbis believe that a minor could have intercourse (younger than that is considered just “playing doctor”). In normal cases a minor cannot marry a woman because he cannot betroth her—betrothal requires “awareness” which he is considered to lack. But this yavam need not “acquire” his wife—she is connected to him by Torah law because the Torah mandates she be married to the brother-in-law. When he has intercourse with her, he now becomes a “minor” husband. We might have thought that his wife is subject to the laws of adultery, therefore the baraita needs to teach us that she is not. But we now do not need to posit that a master can designate a slave woman to his minor son.