TT #646 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:05
When brothers dwell together and one of them dies and has no son, the wife of the dead shall not be outside to a strange man; her husband’s brother shall come upon her and take her to himself as a wife and perform the duty of a husband’s brother for her.
Torah Temimah points to Yevamot 61b / Niddah.
TT lemma: כִּי יֵשְׁבוּ אַחִים יַחְדָּו.
יָבָם קָטָן שֶׁבָּא עַל יְבָמָה קְטַנָּה יִגְדְּלוּ זֶה עִם זֶה; בָּא עַל יְבָמָה גְּדוֹלָה תְּגַדְּלֶנּוּ.
English: A minor yavam who has relations with a minor yevamah — they grow up together; if he has relations with an adult yevamah, she raises him.
On the daf / in context: The verse’s language of “dwelling together” is applied even to the case of minors, establishing that the bond can be created in minority and continues.
Derash applying the verse to minor yavam and yevamah.
Yibbum performed by or with a minor creates a valid bond that continues into adulthood.