Avodah Zarah 37A

הואיל וראוי לביאה, מטמא נמי בזיבה. אמר רבינא: הלכך, הא תינוקת גויה בת שלש שנים ויום אחד, הואיל וראויה לביאה, מטמאה נמי בזיבה.

The Talmud explains the reason for this opinion: Since a 9-year-old boy is fit to have sex, he also imparts ritual impurity as one who experienced ziva. Ravina said: Therefore, with regard to a female non-Jew child who is 3 years and one day old, since she is fit to have sex at that age, she also imparts impurity as one who experienced ziva.

פשיטא! מהו דתימא: האי ידע לארגולי, והא לא ידעה לארגולי? קא משמע לן.

The Talmud asks: Isn’t that obvious? The Talmud explains: It was necessary to state this ruling, lest you say that the halakha that a non-Jew who is suited for sex imparts impurity does not apply to a female. The possible difference between a male and female child is based on the fact that whereas that child, a 9-year-old male non-Jew, knows how to accustom others to sin by employing persuasion, this child, a 3-year-old female non-Jew, does not know how to accustom others to sin until she matures. Therefore, Ravina teaches us that the halakha nevertheless applies to both male and female children.

מיסתמיך ואזיל רבי יהודה נשיאה אכתפיה דרבי שמלאי שמעיה, אמר לו: שמלאי, לא היית אמש בבית המדרש כשהתרנו את השמן. אמר לו: בימינו תתיר אף את הפת! אמר לו: אם כן קרו לן ״בית דינא שריא״! דתנן: העיד רבי יוסי בן יועזר איש צרידה על אייל קמצא דכן, ועל משקה בית מטבחיא דכן, ועל דיקרב למיתא מסאב, וקרו ליה ״יוסף שריא״.

The Talmud relates a relevant incident: R' Yehuda Nesia was traveling while leaning upon the shoulder of R' Simlai, his attendant. R' Yehuda Nesia said to him: Simlai, you were not in the study hall last night when we permitted the oil of non-Jews. R' Simlai said to him: In our days, you will permit bread of non-Jews as well. R' Yehuda Nesia said to him: If so, people will call us a permissive court. As we learned in a Mishnah (Eduyyot 8:4): R' Yosei ben Yo’ezer of Tzereida testified with regard to the eil kamtza, a type of locust, that it is kosher, and with regard to the liquids of the slaughterhouse in the Temple that they are ritually pure, and with regard to one who touches a corpse that he is impure, as soon explained by the Talmud. And as a result, they called him: Yosef the Permissive.