Due to the complex global health, economic and political environments, we are increasingly faced with uncertainties in our daily lives, especially when making decisions. Intolerance of uncertainty (IU) is a trait that describes the extent to which a person is fearful of uncertain situations. IU has been established as a key risk factor for mental health issues; however, the existing studies primarily focus on young adults. Therefore, there is a lack of comprehensive studies examining the effect of age on IU, or its relationship to mental health across the adult lifespan. The current review study addressed this research gap, by systematically reviewing the existing literature on the relationship between aging, IU and mental health. A total of 41 studies were reviewed, of which 32 were examined closely in a meta-analysis. Results suggested a negative correlation between age and IU across the adulthood. This suggested that older adults self-reported a better ability to manage uncertainty in their daily lives than younger adults. However, among the older adults, IU was also found to be a risk factor for poor mental health, considering its significant correlations with anxiety, worry and other mental health problems. Implications of the results for understanding the decision-making tendencies, and interventions for mental health for older adults will be discussed.