Ketubot, Chapter Three, Mishnah Eight
According to Exodus 21:7 a father has the right to sell his daughter into slavery. In interpreting this verse, the rabbis limited this right to when she is a minor, meaning before she both achieves puberty and reaches the age of 12 years [that is to say, one who has reached puberty but is not yet 12 or is 12 but has not reached puberty is still considered a minor]. After this age she is considered a young woman (naarah) and her father may no longer sell her. It is at this age that if she is raped or seduced her father receives a fine. The period in which a woman is considered a naarah can be no longer than six months. After this period, she has reached what was considered to be majority age, and there is no fine incurred by one who rapes or seduces her.
Wherever there is the right of sale there is a fine and wherever there is a fine there is no right of sale.
In the case of a minor there is the right of sale and there is no fine;
In the case of a young woman there is a fine but no right of sale.
In the case of a girl who has reached majority age there is no right of sale and there is no fine.
When a girl is of an age where her father may sell her, according to our mishnah one who rapes or seduces her does not incur a fine. This is learned exegetically from the fact that Deut 22:28 which discusses the fine for rape uses the word naarah. The mishnah concludes that only one who rapes or seduces a naarah incurs the fine and not one who does so to a minor. We should note that according to the Talmud this mishnah is only Rabbi Akivas opinion. The other sages held that one who rapes or seduces a minor is also liable to pay the fine.
When the girl reaches the age of being a naarah, her father can no longer sell her, because Exodus 21:7 refers only to minors. However, at this age one who does rape or seduce incurs a fine.
Finally, six months after becoming a naarah a girl becomes a bogeret, one who has reached majority age. At this point her father loses most of his rights vis a vis her. He can no longer marry her off or sell her. She is legally independent. One who rapes or seduces her does not incur a fine.