This study examined the developmental trajectories of career maturity among Korean youths between late adolescence and mid-20s, and explored how career-counseling experiences, academic achievement, household income, parental involvement, and gender affected their career maturity. We used the 2,362 Youth Panel data collected between 2008-2014 by the Korea Employment Information Service. Career maturity increased linearly over time and decreased gradually after the fourth wave. Multivariate latent growth modeling revealed that a higher intercept of household income, academic achievement, and parental involvement were associated with a higher intercept of career maturity, whereas the effect of these variables on career maturity decreased over time. A higher intercept of career-counseling experiences was related to a higher intercept of career maturity. As the frequency of career-counseling experiences increased rapidly over time, so did career maturity. Career-counseling experiences and household income indirectly affected career maturity through the mediation of academic achievement. The female students' level of career maturity was higher than that of the male students. However, this tendency decreased over time. This study's results of the impact of career counseling on career maturity implies that schools should expand their career education and counseling programs.