Current evidence and research of the life course approach on the association between life experiences and health in old age are fragmentary. This paper empirically examines the "long arm" effect of the childhood circumstances on mental health in later life using a large longitudinal dataset (CHARLS) conducted in 2014 and 2015. We operationalize the childhood circumstances as family economic conditions, community environment, and peer network to include the meaningful content and understand their interaction. The SEM results indicate that effects of those factors contributing to older people's mental health are unequal and vary among age groups and genders. Of those, peer network in childhood determines to a large extent the mental health through the whole life course, while economic conditions and community environment are weakly associated with mental health. Furthermore, we find a distinct interaction mechanism linking those variables. The peer network completely mediates the effect of the community environment on the mental health of older adults and has a partial mediating effect on the economic conditions. Those findings suggest that social policies aimed at promoting older people's mental health in the context of the active ageing and health ageing strategy should go beyond the old age stage and target social conditions early in childhood.
Keywords: active ageing; childhood circumstances; life course; mental health; population ageing.