Based on the play Mary the Third by Rachel Crothers, Wine of Youth concerns Mary (Eleanor Boardman), a flapper whose mother (Eulalie Jensen) and grandmother (Gertrude Claire) were also named Mary. The first two Marys worked all their feminine wiles to snare their husbands, but the youngest Mary doesn't know if she really wants to be tied down. Two young men vie for her hand: sweet natured Lynn (Ben Lyon) and the charming but aggressive Hal (William Haines, playing the type of character that would later make him famous). Mary can't choose between the two of them, so, after a wild party, she decides to take them both on a camping trip, along with her pal, Tish (Pauline Garon), and Tish's sweetheart, Max (William Collier Jr.). Tish and Max decide to "do the right thing" and get married. It doesn't take long for Mary, meanwhile, to disqualify the pushy Hal, and insist that the party return home. When Mary enters her house she overhears her mother and father (E.J. Ratcliffe) arguing over her escapade, and she believes that they no longer love each other. This revelation causes her to lose all faith in the institution of marriage. Her mother decides to leave. When she faints, her husband believes she has been poisoned. This makes him realize how much he really does care. When Mary sees this she decides to accept Lynn's proposal.