The present study explored how romantic relationship qualities develop with age and relationship length. Eight waves of data on romantic relationships were collected over 10.5 years during adolescence and early adulthood from a community-based sample in a Western U.S. city (100 males, 100 females; M age Wave 1 = 15.83). Measures of support, negative interactions, control, and jealousy were derived from interviews and questionnaire measures. Using multilevel modeling, main effects of age were found for jealousy, and main effects of relationship length were found for each quality. However, main effects were qualified by significant age by length interactions for each and every relationship quality. Short relationships increased in support with age. In comparison, long-term adolescent relationships were notable in that they were both supportive and turbulent, with elevated levels of support, negative interactions, control, and jealousy. With age, long-term relationships continued to have high levels of support, but decreased in negative interactions, control, and jealousy. Present findings highlight how the interplay between age and relationship length is key for understanding the development of romantic relationships.