Das Einhorn (1978)

A copywriter gets famous with his first book. When asked to write a new novel about love for his publisher, he urgently needs tutoring since he doesn't know the first thing about it. His way through the beds leads him to the very young Orli. In her he discovers the true meaning of love, which makes him forget all the wrong paths of the past decades and feel young again.

Unfortunately the movie Das Einhorn is not yet available on HBO Max.