In drawing on analyses of trial records involving underage boys and girls, codes, and legal treatises, this paper explores how legislators, doctors, lawyers, jurors, and social workers were influenced by late-nineteenth to mid-twentieth century understandings of age, gender, and sexuality as they framed the legal categorization of statutory rape—defined as criminalized sexual activity with a minor—in Mexico City from the late Porfiriato to 1950. In analyzing the legal developments in the country’s civil, criminal, and penal laws such as the Federal Penal Code of 1896, the Civil Code of 1928, and the Mexican Criminal and Penal Codes of 1929, this paper analyzes how legal officials and bureaucrats interpreted legal conceptions of violent activities within and outside the confines of family life. I will argue that assumptions of age, gender, and sexuality of the suspects and victims served as a framework to establish a legal regime of age grading in an attempt to define childhood with juridical and legal boundaries. Ultimately, this study reveals how the underlying mechanisms of criminal and family law contributed to highly contested disputes over both the boundaries of childhood and age of consent affecting the legal outcomes of statutory rape, the number of trials that were dismissed, and those that ended in acquittals or convictions during the mid-twentieth century.