The 15 Year Old Girl(1989)

Willy, a middle-aged divorcee, decides to take his 15 year-old son, Thomas, on holiday to Ibiza, staying at an isolated villa on the unspoilt part of the coast. Thomas insists on bringing his friend Juliette, a girl of his own age with whom he enjoys a close platonic relationship. When it comes to physical love, Juliette is wise beyond her years. She will only sleep with men older than herself and has no intention of committing herself to a long-term relationship.