This article examines the attempted impeachment of the duke of Buckingham by parliament in 1626 through the lens of manhood, and specifically early modern definitions of youth. The parliamentary speeches of Buckingham's accusers and the reports of observers such as the Venetian ambassador are used to demonstrate how youth and inexperience were deployed as evidence of his insufficient manhood, and therefore legal justifications for Buckingham's removal from power. The attributes of youth – wilfulness, rashness, and being a prisoner to one's passions – provided a narrative in which Buckingham could be placed to discredit his political authority. Additionally, through personal correspondence with his allies, and Buckingham's own defence of himself before parliament, this article demonstrates that definitions of youth and its relationship with political authority were malleable in the early modern period. Buckingham's impassioned defence of both his political career, and himself as a man, point to an ongoing negotiation over the terms of manhood, and how men were judged as figures of legitimate political authority.