Sweet 18 reminded myself of It Started with a Kiss. It has the same feeling around it, and has a silly main girl pursuing the boy. It's not exactly the same that you are asking but I think you might like it.
As for other recommendations, here are some that involve marriage and/or age difference:
- Nagareboshi - older male, yonger female and marriage contract,
- Full House - contract marriage,
- Wonderful life - forced marriage because of one night stand,
- Drunken to Love you - contact marriage (same director of Fated to Love You TW),
- Kou Kou Kyoushi 2003 - teacher/student relationship,
- Innocent Love - younger girl, older male.
I hope you can find something good to watch. :D