Lola aka Twinky (1970)
IMDb synopsis:
Scott Wardman (Charles Bronson), a 40-year-old writer of pornographic novels, meets and falls in love with 16-year-old schoolgirl Twinky (Susan George). This alone is cause for concern, but, when the couple get married and move to America, the trouble and fun really begin.

Breezy (1973)
IMDb synopsis:
Breezy (Kay Lenz) is a teenage hippy with a big heart. After getting a ride with a man who only wants her for sex, Breezy manages to escape. She runs to hide on a secluded property where stands the home of middle-aged, divorced Frank Harmon (William Holden). He reluctantly takes Breezy in, only to fall unexpectedly in love with her.
http://www.imdb.com/title/tt0069822/

Circle of Two (1981)
IMDb synopsis:
The story of the impossible love between a schoolgirl (Tatum O'Neal) and a 60-year-old painter (Richard Burton).
Circle of Two (1981) - IMDb (http://www.imdb.com/title/tt0080536/?ref_=fn_al_tt_1)

Ghost World (2001)
IMDb synopsis:
This is the story of Enid (Thora Birch) and Rebecca (Scarlett Johansson) after they finish the high school. Both have problems to be related with people and they spend their time hanging around and bothering creeps. When they meet Seymour (Steve Buscemi), a social outsider who loves to collect old vinyl records, Enid's life will change forever.
Ghost World (2001) - IMDb (http://www.imdb.com/title/tt0162346/?ref_=fn_al_tt_1)

Age of Consent (1969) ~ They don't have a relationship, but she wants one.
IMDb synopsis:
An elderly artist (James Mason) thinks he has become too stale and is past his prime. His friend and agent persuades him to go to an offshore island to try once more. On the island, he rediscovers his muse in the form of a young girl (Helen Mirren).
http://www.imdb.com/title/tt0063991/?ref_=fn_al_tt_1