"Under 18" is a charming pre-Code film that includes the best of the genre: beautiful art deco sets, stunning period fashions, and scenes that were titillating for their time.
According to notes in the bio of Ms. Marsh, the film was not a critical success, but I do not understand why. The film's best asset is the performance of Marian Marsh herself, who is cute as a Kewpie doll. She plays Margie, a seamstress in the back room of Maison Ritz--a couture fashion house--where she is enthralled by the happenings in the front salon, where rich men bring their women to select expensive gowns and furs.
Margie's friends and relatives exist on the lower end of the financial spectrum, trying to get ahead. Her boyfriend, Jimmy, is an optimist. He always tells her that good times are just around the corner. But when times get worse, Margie is tempted to take a short cut.
In 1931, as skyscrapers captured the imagination of the public, it must have felt like there were two worlds--the life of penthouse luxury that existed in the sky and the life of the hoi polloi down on street level. This film captures that concept very well (similar to Fitzgerald's vision of a distant, unattainable East Egg in "The Great Gatsby").
There is nothing about this film that I would criticize. It offers a wonderful view of the life and times of the early thirties, including the changing mores that some saw as opportunity and others saw as the demise of traditional values.