Previous longitudinal studies of personality in adulthood have been limited in the range of traits examined, have chiefly made use of self-reports, and have frequently included only men. In this study, self-reports (N = 983) and spouse ratings (N = 167) were gathered on the NEO Personality Inventory (Costa & McCrae, 1985b), which measures all five of the major dimensions of normal personality. Cross-sectional and longitudinal analyses on data from men and women aged 21 to 96 years showed evidence of small declines in Activity, Positive Emotions, and openness to Actions that might be attributed to maturation, but none of these effects was replicated in sequential analyses. The 20 other scales examined showed no consistent pattern of maturational effects. In contrast, retest stability was quite high for all five dimensions in self-reports and for the three dimensions measured at both times in spouse ratings. Comparable levels of stability were seen for men and women and for younger and older subjects. The data support the position that personality is stable after age 30.
Costa, P. T., &McCrae, R. R. (1988). Personality in adulthood: a six-year longitudinal study of self-reports and spouse ratings on the NEO Personality Inventory. Journal of personality and social psychology, 54(5), 853.