Age and gender differences across the lifespan in dark personality features could provide hints regarding these features’ functions. We measured manipulation, callous affect, and egocentricity using the Dirty Dozen and their links with agreeableness in a pooled cross-sectional dataset (N = 4292) and a longitudinal dataset (N = 325). Age trends for all dark personality features were progressive through adolescence, but negative through adulthood. Men scored higher than women, but the gender gap varied with age. Trends for agreeableness partly mirrored these trends and changes in dark personality features and agreeableness were correlated. Results are discussed in light of the maturity principle of personality, gender role socialization processes, and issues regarding incremental validity of dark personality over traditional antagonism measures.