Give me a frigging' break!
Movies about older men and women having real or imagined relationships with younger members of the opposite sex have been around for ever.
As far as "promoting" polyamory, we can start proportioning blame by assigning Joseph Smith his fair share.
Name one film in the "forever" past that had an adult man or woman engaging in love making with a member of the opposite or same sex at the ages of 12-16? NAMES THEM!!