Yevamos 10:8 - 10:9

בן ט' שנים ויום אחד שבא על בימתו ומת חולצת ולא מתיבמת – for she upon her the interdependence of a childless widow and her late brother’s brothers (i.e., the levirate relation) two brothers-in-law for the act of coition of this one, the younger (i.e., nine days and one-day old) is like the statement of levirate marriage from the older. She does not leave the levirate relation of the falling of the first [brother], and there falls upon her the levirate relationship through the falling of the second [brother] (see Rashi on the concluding Mishnah in Tractate Yevamot 96b). But it is taught in the Mishnah in Chapter Three (“Four Brothers”) (Tractate Yevamot, Mishnah 9, [referring to] the one who is subject to the levirate power of a single brother-in-law, and not the one who is subject to the levirate power of two brothers-in-law.

נשא אשה – [he married a woman] who is not his sister-in-law (i.e., the widow of the deceased childless brother), and he has brothers,

הרי זו פטורה – she is exempt, even though his sexual coition (i.e., of the brother who is nine years and one day old) is considered coition but his acquisition is not an acquisition at all until he brings forth two [pubic] hairs. But the widow of the childless dead brother, since she is dependent upon him, the Rabbis made her like a statement of betrothal.

אם לא ידע הראשונה משהגדיל ראשונה חולצת ולא מתיבמת – for the levirate relationship of two levirs is upon her, for since he did not know her [sexually] once he grew up, she did not leave from the first falling [of the levir to her].

רבי שמעון אומר מיבם לאיזה שירצה – for Rabbi Shimon does not hold by the levirate relationship of two levirs , and these words, we mentioned in the chapter of “Four Brothers” (Tractate Yevamot, Chapter 3, Mishnah 9).

וחולץ לשניה – for they are not rival wives to exempt one of them with the levirate marriage of her colleague. But a levirate marriage of both of them does not occur since she is her rival wife as part of the statement of levirate marriage of the Rabbis, but it appears as two widows of a brother who died without issue who come from one house.

אחד בן תשע ואחד בן כ' – both are equal for everything mentioned above, for as long as they haven’t brought forth two [pubic] hairs, he is a minor. Until he will be thirty five years of age and if he arrive at the thirty five years and did not bring forth two [pubic] hairs, even though they didn’t appear on him, they are a sign of his being castrated/a eunuch that is explained above (see Tractate Yevamot, Chapter Eight, Mishnah Four) – which is that of a natural eunuch.