Harold and Maude (1971)

This cult classic film flips the gender roles in traditional age gap relationships. Suicidal Harold, played by 23-year-old Bud Cort, forever changes his outlook on life when he meets Maude, played by 75-year-old Ruth Gordon. The 52-year-old age gap is the largest on this list, and the film explores the taboo relationship to great lengths. Although the film's reputation has increased with time, it received harsh reviews from critics when it released. Famously, Variety described the film as "funny as a burning orphanage."