This study investigated the impact of getting older than the mean marriage age on mental disorders and suicidality among never-married people. We performed an epidemiological survey, a nationwide study of mental disorders, in 2016. In this study, a multi-stage cluster sampling was adopted. The Korean version of the Composite International Diagnostic Interview was conducted with 5,102 respondents aged 18 years or above. The associations between never-married status, mental disorders, and suicidality were explored according to whether the mean age of first marriage (men = 32.8 years; women = 30.1 years) had passed. Never-married status over the mean marriage age was associated with agoraphobia, obsessive-compulsive disorder, mood disorders, and major depressive disorder after adjusting for sociodemographic factors. Respondents with never-married status above the mean marriage age were associated with suicide attempts (adjusted odds ratio [aOR], 3.21; 95% confidence interval [CI], 1.36-7.60) after controlling for sociodemographic factors and lifetime prevalence of mental disorders, while respondents with never-married status under the mean marriage age were not. Moreover, in respondents with never-married status, getting older than the mean marriage age was associated with suicidal ideations (aOR, 1.49; 95% CI, 1.04-2.15) and suicide attempts (aOR, 3.38; 95% CI, 1.46-7.84) after controlling for sociodemographic factors and lifetime prevalence of mental disorders. Never-married status above the mean first marriage age was associated with mental disorders and suicidality. These findings suggest the need for a national strategy to develop an environment where people with never-married status do not suffer even if their marriage is delayed. © 2020 The Korean Academy of Medical Sciences.