Alice falls in love with her adopted father and courts him when she comes of age.
Alice and Bob are in an Arranged Marriage in which neither had any say, and both of them are so weirded out by the age difference that they never consummate it.
Subverted: Bob begins to court Alice when she comes of age but she is so repulsed by the idea that she rejects him.
But eventually Alice realizes that no one has ever loved or cared about her more than Bob and comes to accept his advances. Things proceed from there.
Bob has known Alice since she was a small child, and when she turns of age, they begin courting. But Bob eventually puts a stop to the relationship, and sets her up with a nice young man. Turns out, Bob's a time traveler and this nice young man is Bob's younger self. ( ...and so isthe girl)
Parodied: Bob is a loner who can't get a date. Bob declares his undying love for Alice when she's only 5, yet she's sane enough to be weirded out by the idea. Flash forward a year, where the same declaration is made, with identical results. Repeat for fifteen years, during which Bob never ages (or change his clothes) and Alice sports the same weirded-out look on her face.
Zig Zagged: Bob is like a father to Alice. As she gets older people start to suspect that he has a romantic interest in her, and is raising her to be the ideal wife. When confronted w/ this Bob denies it, and seems squicked out by the idea. Then it turns out he has been raising her to be the ideal wife for his son, Charlie (who is 7 years younger than Alice).
Averted: Bob does not view Alice as anything more than a child and makes no advances towards her.