In almost every decade, Hollywood produces films that threaten to explore important issues of their day, including changes in gender roles. And most of those films are bits of fluff. Many of these films also promise--with their trailers--to titillate. Consider the films of Doris Day and Rock Hudson. With a title like "Pillow Talk", the viewer might reasonably expect two people talking in the same room. Or how about those split screens that suggest a couple simultaneously in a bathtub.
In 1968 there were plenty social movements to tackle--the war, race relations, sexual empowerment. "The Impossible Years" is the story of a teenage girl whose sexual experience is the concern of her parents. Like other films, it nibbles around the edges of the topic with occasional "edgy" moments like mentioning that she's now a "C cup".
But this is s comedy and no real issues must interfere with the wackiness. Unfortunately, this film (like most of its time) comes from the Erma Bombeck school of comedy--a slapstick style that takes farce and reduces it merely to scenes of bedlam. People trip, they swing things at each other, they slam doors.
The opening credits are accompanied by the eponymous song by The Cowsills--an unfortunate pairing. I like The Cowsills. Their version of "Hair" is catchy and evokes the time period. But they also sang the theme song for "Love American Style", which also was a catchy tune, but here it forms a thematic bridge between that pseudo-titillating series about romantic relationships and this film, further reminding the viewer that he can expect nothing but pap and silliness.
Even David Niven as the father cannot save the film from its mediocrity. He represents the older generation and father and daughter are meant to talk past each other more than to each other.