Age-Graded Stability and Change in Dark Triad Traits: Seven-Wave Evidence From a Large Japanese Panel, With Big Five Benchmarks.

OBJECTIVE: Dark Triad longitudinal evidence outside Western samples is sparse, and age moderation is typically polynomial, obscuring age-specific patterns. METHOD: We described stability and mean-level change in Dark Triad and Big Five traits in a Japanese seven-wave panel (FY18-FY24; N = 188,296; 66,529 with two or more waves; ages 15-102). Dark Triad was modeled as parcel-level latent variables (SD3-J); TIPI-J indexed Big Five benchmarks. Kernel-weighted local SEM estimated stability and growth across focal ages 20-75. RESULTS: Parcel-level scalar invariance held across all 138 focal-age × gender × scale cells. Lag-1 stability rose with focal baseline age, steepest for Machiavellianism. Narcissism and Psychopathy slopes were more positive at younger ages, attenuating by the mid-sixties; Machiavellianism briefly declined. Big Five curves showed sign reversals for Agreeableness and Conscientiousness, declining Openness, and rising Emotional Stability. Age-resolved gender comparisons surfaced slope differences hidden by pooled summaries, notably for Psychopathy. Change covaried for Narcissism and Psychopathy but not Machiavellianism, whose correlation with Narcissism reversed sign with age. CONCLUSIONS: Dark Triad traits neither changed alike nor changed together, Machiavellianism standing apart; Agreeableness and Conscientiousness departed from maturity-principle expectations at younger but not older ages. Interpretation is provisional given age-cohort-period confounds and two-item measurement.