1,868. Minors and Yibum
Yibum v’Chalitzah 1:16
As we discussed in Hilchos Ishus 11:3, sexual intimacy performed by a boy nine years and one day old has halachic consequences; this law was transmitted by oral tradition. Therefore, if a surviving brother who is still a minor but older than nine performs yibum*, he reinforces their bond (to the exclusion of any other of the deceased’s widows or brothers). One may not, however, perform chalitzah until one has reached the age of majority and displays the signs of maturity. This is because the Torah specifies “man” regarding chalitzah (Deuteronomy 25:7). Below the age of nine, sexual intimacy carries no halachic efficacy; even the relations of a nine-year-old are not completely binding. Therefore, the yevama may not marry anyone else until he has relations with her after reaching the age of majority or performs chalitzah, as we will see in chapter 5.
Yibum v’Chalitzah 1:17
The same is true of a yevama who is a minor: yibum may be performed* but chalitzah may not until she reaches the age of majority and displays the signs of maturity. Even if she engaged in sexual intimacy after reaching the age of 12, she may not perform chalitzah until she is inspected and displays the physical signs of maturity.
*This is not to advocate that such things should be done; the halacha is only discussing the legal ramifications if these circumstances should happen to occur.