Set on campus (with lots of nostalgic school songs on the soundtrack), YOUTHFUL LUST is notable for having a main character much older than the usual porn studs prevalent back then and now.
What looks like guerrilla filmmaking footage of people on the campus grounds leads to the story of Pete and his girl friend, visited by Pete's dad (Peter Sr.). Daddy catches them in the bedroom in the act of fellatio, to which Jr. merely says "This is Harriet".
Harriet gets to stay with her friend Brigitte Maier, hot as always. With Pete and buddy Jerome visiting they have a four-way, but later Pete feels guilty about the orgy.
While Harriet is getting it on later alone with Jerome, Maier visits Pete Sr. at the dorm and they have a surprisingly serious discussion about sex, Harriet and the generation gap. Brigitte talking dirty angers Pete St., but he embarrassingly gets a hard-on in her presence. He can't resist her, and as a chorus sings "I want a girl just like the girl that married dear old dad" she gives him a blow job, and then they hump.
Pete Jr. interrupts them, cuing lots of exposition and dumb twists: Pete Sr. gets divorced, Jr. takes over daddy's business in Phoenix, and Sr. takes up living in Jr.'s former apartment.
Harriet visits and next twist has Sr. hooking up with her, as the Whiffenpoof Song plays. After he shoots on her posterior, Harriet gives him an A+, and they move in together, finalizing a cheerful May/December romance.
Story progression is unusual, making this watchable.
So it turns out the "ful" in the title is the key syllable, as we are treated to the novelty of a middle-aged guy taking over center stage from the youngsters in a sex film, and treated somewhat sympathetically -perhaps reflecting the subconscious desire of the auteur "John Mirisch". Clearly Lenny Kirsch as Pete Sr. enjoyed the opportunity to star in a porno film, after which he probably went back to his day job.
