1,430. A Ketana and a Naarah

Hilchos Ishus 1:8

Certain relations are prohibited as a consequence of positive commandments. There are three such relations: the first and second generations of converts from Egypt and Edom – both men and women – and a woman who is not a virgin to a Kohein Gadol. No verse overtly prohibits such relations. Rather, the prohibition against converts from Egypt and Edom is inferred from Deuteronomy 23:9, which says that these may enter the general marriage pool in the third generation, from which we see that the first and second generations may not do so. Similarly, Leviticus 21:13 obligates the Kohein Gadol to marry a virgin, from which we infer that he may not marry a non-virgin. A prohibition that is inferred from an obligation is considered an obligation.

Hilchos Ishus 2:1

From the day a girl is born until she is 12 years old, she is called a ketana or a tinokes (i.e., a minor). Even if she grows multiple pubic hairs during this period, they are of no legal significance. If she grows two pubic hairs after reaching 12 years of age, then she is called a naarah (maiden).