Tell the children of Israel: When a man (אִישׁ) or woman commits any of the sins against man to act treacherously against God, and that person is [found] guilty
and Levi, who was 13 at the time, was called a man when he attacked Shechem (Bereshit 34:25):
וַיְהִי בַיּוֹם הַשְּׁלִישִׁי בִּהְיוֹתָם כֹּאֲבִים וַיִּקְחוּ שְׁנֵי בְנֵי יַעֲקֹב שִׁמְעוֹן וְלֵוִי אֲחֵי דִינָה אִישׁ חַרְבּוֹ וַיָּבֹאוּ עַל הָעִיר בֶּטַח וַיַּהַרְגוּ כָּל זָכָר
Now it came to pass on the third day, when they were in pain, that Jacob's two sons, Simeon and Levi, Dinah's brothers, each (אִישׁ) took his sword, and they came upon the city with confidence, and they slew every male.
Rashi on Nazir 29B says that we don't find anyone under 13 called a man (אִישׁ) in the Torah, but Shimon and Levi who were 13, were called men (אִישׁ) when they attacked Shechem.
How do we know that a girl becomes Bat Mitzvah at 12 years old? Is there a passuk where we refer to a girl as a woman (אִשָּׁה), and we know that she was only 12?