Of course, this window of opportunity bears about as much resemblance to reality as Pokemon does to animal husbandry.
The numbers are arbitrary and invented and almost always tend to be pulled from thin air; I’ve had statistics when it comes to sex and relationships.
For this trope's impact on relationships, see Unsettling Gender Reveal, Jumping the Gender Barrier and Gender-Bender Friendship.
Contrast with Transsexual and Hermaphrodite, which are real-life phenomena (though on rare occasions, a Gender Bender character might a hermaphrodite instead of, strictly speaking, the "opposite sex"; also, Gender Bender stories can intersect with transsexual characters, by having someone transition unexpectedly by magic, or have the experience of being gender-changed bring a transsexual character out of denial.
Of course that then leads to the question of just For a lot of men, the anxiety surrounding their dating inexperience can be overwhelming.
They become intimidated by women whom they fear have more experience than they do.
Her weight may not even be (and, in most cases of the trope probably won't be) the basis of her beauty or attractiveness; attention may instead be drawn to her beautiful eyes, feminine features or, more blatantly, her breasts or posteriorbut regardless, she is a knock-out.