Background Childhood health significantly influences mental well-being in later life, but this relationship remains underexplored in China. This study aims to investigate the long-term associations between childhood health status and depressive symptoms in older adults, emphasizing the need for early interventions to promote lifelong mental health. Methods We utilized data from a nationally representative survey conducted across 28 provinces of China, comprising 15,581 adults aged 45 years and older. Depressive symptoms were assessed using the Center for Epidemiological Studies Depression scale. Logistic regression and decision tree models were applied to examine the association between childhood health and depressive symptoms in later life. Results The overall prevalence of depressive symptoms among participants was 33.75%. Those reporting excellent or very good childhood health had a lower prevalence (29.99%), while those with poor childhood health reported a markedly higher rate (47.57%). After adjusting for demographics and lifestyle factors, poor childhood health was associated with a higher likelihood of depressive symptoms (AOR 1.83, 95% CI 1.56-2.14, P < 0.0001). Other risk factors included aged 65-74 years (AOR 1.23, 95% CI 1.10-1.38, P = 0.0009), female gender (AOR 2.01, 95% CI 1.78-2.28, P < 0.0001), and never drinking (AOR 1.24, 95% CI 1.11-1.38, P = 0.0012). Protective factors included tertiary education (AOR 0.45, 95% CI 0.32-0.65, P = 0.0030), higher BMI (BMI 24-27.9 kg/m(2): AOR 0.72, 95% CI 0.60-0.87 kg/m(2), P = 0.0033; BMI >= 28 kg/m(2): AOR 0.69, 95% CI 0.56-0.85 kg/m(2), P = 0.0030), sleep duration of seven or more hours (7-10 h sleep: AOR 0.52, 95% CI 0.48-0.57, P < 0.0001; >= 10 h sleep: AOR 0.50, 95% CI 0.43-0.58, P < 0.0001), never smoked (AOR 0.77, 95% CI 0.68-0.86, P < 0.0001), and urban residency (AOR 0.57, 95% CI 0.50-0.64, P < 0.0001). The decision tree model highlighted key factors associated with depressive symptoms, including childhood health, non-communicable diseases, sleep duration, residency, alcohol consumption, and smoking status. Conclusions Our findings suggest that childhood health may influence mental well-being in later life. Promoting healthy behaviors from early childhood could help reduce depression risk in older age. However, the reliance on self-reported data and a cross-sectional design limit causal interpretation. Preventive care and targeted interventions for vulnerable children should be prioritized to improve long-term mental health outcomes.