Background: While advanced age is a known risk factor for postoperative complications following hip arthroplasty, its role as an independent predictor versus a surrogate for comorbidity remains unclear, particularly in developing countries. This study aimed to investigate the independent impact of age on postoperative outcomes and explore the mediating role of key comorbidities in a resource-limited setting. Methods: We retrospectively reviewed 769 adult patients undergoing hip arthroplasty at a Vietnamese tertiary hospital (2021–2024), categorized into three groups: younger adults (18–64 years), older adults (65–79 years), and oldest old (≥80 years). The primary outcome was a composite of major postoperative complications. Multivariable logistic regression and structural equation modeling were used to identify independent predictors and assess mediation effects. Results: Among 769 patients, 363 were younger (47.2%), 241 older adults (31.3%), and 165 oldest old (21.5%). Complication rates increased significantly with age (18.7%, 36.9%, and 60.0%, respectively; p<0.001). However, multivariable adjustment showed that age was not an independent predictor. Instead, heart failure (adjusted odds ratio [aOR]=5.49, 95% confidence interval [CI] 2.19–13.74) and preoperative anemia (aOR=1.77, 95% CI 1.21– 2.59) were identified as independent risk factors. Mediation analysis revealed that the effect of age on complications was significantly mediated through preoperative anemia. Conclusion Increased postoperative risk in older adults is driven by comorbidity burden rather than chronological age. Preoperative anemia and heart failure are critical, independent predictors, with anemia acting as a key mediator for the effects of age. Individualized correction of modifiable comorbidities may be more beneficial than using age alone to assess surgical risk.