פירוש על קידושין 7:21

The argument here is getting more complex. We might have thought that a girl who will never reach na’arut, meaning she will never hit puberty could not be sold. After all, if she goes free at na’arut then maybe if she will never be a na’arah, meaning she is an aylonit who will never hit puberty, then she could not have been sold in the first place. Therefore, we have a verse that says (midrashically) that an aylonit goes out of slavery at bagrut (age 20). This teaches us that she can be sold in the first place.

"If the signs of na'arut have not arrived, then the sale would be invalid". [Problem:] But if you say: While she is a minor, how would we know that she would not produce the signs of na'arut since the signs of being an aylonit are if she is 20 years old and hasn't produced 2 hairs, as is in chapter Ha-Arel (Yevamot 80b)!? [Additional layer to the problem:] And even though there are signs of being an aylonit that are possible to recognise while she is a minor, such as a thick voice and her lower abdomen is not like those of women, we say regarding a eunuch: "Until he should have all of [the signs he is not considered a eunuch", and we would assume that this is the case also for an aylonit! Solution: This is what it meant to say: "The sale is invalid" and the master needs to return her handiwork and the father should return the money [so you can wait until all the signs of an aylonit are there and then retroactively undo the sale]. This all would be the case also if she were designated [and sold as a wife to a freeman, and not just sold for her handiwork, the sale would be disqualified].