Commentary for Kiddushin 7:19

Abaye points out that not all girls who reach majority age will actually go through “na’arut.” “Na’arut” is more than just hitting 12. It is hitting 12 and developing signs of puberty. A girl can become a bogeret at the age of 20 without ever hitting puberty. Such a girl is called an “aylonit” (we learned the term in Ketubot—it is sometimes translated as barren, but women can hit puberty and be barren. Still an aylonit is by definition barren). If only one word had been taught I might have thought that only a bogeret who had hit puberty would go free. Therefore, the second word teaches that a na’arah goes free, and a bogeret who never becomes a na’arah also goes free (although only at a later age).