Do others perceive the personality changes that take place between the ages of 14 and 29 in a similar fashion as the aging person him- or herself? This cross-sectional study analyzed age trajectories in self- versus other-reported Big Five personality traits and in self-other agreement in a sample of more than 10,000 individuals from the myPersonality Project. Results for self-reported personality showed maturation effects (increases in extraversion, conscientiousness, openness to experience, and emotional stability), and this pattern was generally also reflected in other-reports, albeit with discrepancies regarding timing and magnitude. Age differences found for extraversion were similar between the self- and other-reports, but the increase found in self-reported conscientiousness was delayed in other-reports, and the curvilinear increase found in self-reported openness was slightly steeper in other-reports. Only emotional stability showed a distinct mismatch with an increase in self-reports, but no significant age effect in other-reports. Both the self- and other-reports of agreeableness showed no significant age trends. The trait correlations between the self- and other-reports increased with age for emotional stability, openness, agreeableness, and conscientiousness; by contrast, agreement regarding extraversion remained stable. The profile correlations confirmed increases in self-other agreement with age. We suggest that these gains in agreement are a further manifestation of maturation. Taken together, our analyses generally show commonalities but also some divergences in age-associated mean level changes between self- and other-reports of the Big Five, as well as an age trend toward increasing self-other agreement.