Background: Age is a known prognostic factor for various cancers. However, few studies explored the association between age and prognosis of esophageal cancer (EC) comprehensively, especially from a nonlinear perspective. Design: Retrospective cohort study. Objectives: Our study aims to explore the possible nonlinear associations between age and prognosis in EC patients receiving curative surgery and radiotherapy, respectively. Methods: Cox regression models with restricted cubic splines were used to model the possible nonlinear relationship between age and prognosis in surgical and radiotherapy groups, respectively. Surveillance, Epidemiology, and End Results database was used to validate the age-prognosis patterns found in Jing-Jin-Ji Esophageal and Esophagogastric Cancer Radiotherapy Oncology Group database. Age-prognosis patterns were further validated by survival comparisons between different age subgroups and in subsequent sensitivity and subgroup analyses. Primary endpoint is overall survival. Secondary endpoints are cancer-specific survival and progression-free survival. Results: A total of 56,457 patients from two large cancer databases were included. Patients receiving surgery and radiotherapy showed two distinct nonlinear age-prognosis patterns. Age showed a U-/J-shaped association with prognosis in the radiotherapy group, with a nadir at approximately 65- to 70-years-old. As for surgical cohort, relative risk for all-cause mortality and cancer-specific mortality increased with age with p for nonlinearity <0.05. The above age-prognosis relationships were validated by sensitivity, subgroup, and comparative survival analyses. Youngest and middle-aged patients showed better survival results compared to that of other age subgroups in surgical and radiotherapy cohorts, respectively [Radiotherapy, youngest/middle: hazard ratio (HR) = 1.06, 95% confidence interval (CI): 1.02-1.10, p = 0.001; Radiotherapy, oldest/middle: HR = 1.21, 95% CI: 1.18-1.24, p < 0.001; Surgical, middle/youngest: HR = 1.19, 95% CI: 1.14-1.25, p < 0.001; surgical, oldest/youngest: HR = 1.85, 95% CI: 1.75-1.97, p < 0.001]. Conclusion: Patients receiving surgery and radiotherapy showed two distinct age-prognosis patterns. Younger and middle-aged patients were associated with better survival in surgical and radiotherapy groups, respectively. Additional studies are warranted to explore the underlying mechanisms and clinical implications of this phenomenon.