Such a screenplay or story should have a degree of humor in it, but not at the point of ever getting silly or becoming a true comedy (a "dramedy" would be fine). It should treat the topic in a gentle way, and have both participants in the intergenerational affair as much like average people as possible, i.e., flawed individuals but basically decent. It should not seek to preach, but simply to evoke understanding and sympathy, and yes it should end in an "indecisive" manner. And yes, PLEASE stay away from the incestual relationship theme that so many GLers appear to be fascinated with, as it won't go off well in today's climate, and would be an entirely different type of film; let's tackle one type of controversy at a time.
I recommend that everyone who wants to compose a good screenplay on this subject locate and watch the too-little-known but excellent and positive, if indecisive at the end, 1979/1980 film gem about intergenerational love titled A Circle of Two with Tatum O'Neil and Richard Burton, both of whom gave excellent performances as a 15-year-old girl and a 60-year-old artist who fall in romantic love with each other. Such a movie hasn't been made since then, and it's about time one is.