Background: The extent to which predictors of return to work (RTW) and recurrence of work disability episodes vary by age group is not well understood. Methods: We examined the associations of sociodemographic and clinical factors with RTW and recurrence after mental-disorder-related work disability episodes in a cohort of 10,496 Finnish public sector employees. Disability records were derived from national disability registers between 2005 and 2011. Effect modification by age was examined in age groups of 21–34, 35–50 and >50 years. Results: A total of 16,551 disability episodes from mental disorders were recorded. The likelihood of RTW was elevated in age group 21–34 (hazard ratio (HR) = 1.36, 95% confidence interval (CI) = 1.28–1.46) and 35–50 years (HR = 1.22, 95% CI = 1.18–1.26) compared to age group >50 years. The risk of a recurrent episode of work disability was higher in age groups >50 (HR = 1.29, 95% CI = 1.09–1.52) and 35–50 years (HR = 1.20, 95% CI = 1.03–1.41) compared to the youngest age group. Employees with depressive disorders were less likely to RTW than employees with neurotic, stress-related and somatoform disorders, and this difference increased with age. Low education was associated with increased risk of recurrent work disability episode in age groups of 50 years or younger, while no such association was observed in age group >50 years. Conclusions:The importance of depressive symptoms over neurotic, stress-related and somatoform disorders as predictors of delayed RTW increases with age, whereas educational differences in the recurrence of an episode diminish by age.