If the genders were reversed, people (especially feminists) would be calling the man a sick, old pervert. However, the older charactet is in fact a woman, so the sexist hypocrites think the relationship is "cute." Typical double standards. But, like i said, this IS a classic with brilliant Cat Stevens tunes.
in the past i've always been bringing up 1985's Creator with Peter O'Toole and Mariel Hemmingway as a role reversal version of Harold & Maude of sorts, but your comment about "teaching" gives me pause to reconsider as in that film while O'Toole is the elder, he really has stopped 'living' so to speak. It's the younger Hemmingway who teaches him to live life.
I'm pretty much a feminist most of the time but I hardly ever care if there is an old man and a young woman. Just as long as its a healthy relationship. But maybe I'm a rare creature.