Background: The incidence of endometrial cancers is increasing overall and among women younger than 50 years in the U.S. Younger women tend to present with earlier stage and lower grade histology than older women but may be less likely to receive adjuvant treatment for high-risk disease. Age-related differences in clinicopathologic features and treatment may be influenced by access to care in the general population, which is standardized in the Department of Defense (DoD) Military Health System (MHS) in the United States. We aimed to examine differences in tumor characteristics, surgical management, and adjuvant therapy by age group in this universal access setting. Methods: This retrospective cohort study used the Military Cancer Epidemiology (MilCanEpi) database, which links the DoD cancer registry and medical claims data, to identify women diagnosed with endometrial cancer from 2001–2014 who underwent hysterectomy within 6 months of diagnosis. Modified Poisson regression estimated adjusted risk ratios (ARRs) for advanced tumor stage (II, III, or IV vs. I), aggressive histologic subtypes [high-grade endometrioid endometrial carcinoma (EEC) or non-EEC vs. low-grade EEC], surgical management, and adjuvant treatment (chemotherapy or radiation) by age at diagnosis: 18-49, 50-64, and >65 years. Results: Among 1,223 patients, 16% were aged 18–49, 61% aged 50–64, and 23% aged ≥65. Compared to women aged 50–64, those aged 18–49 were less likely to have aggressive histologic subtypes (ARR=0.65; 95% CI=0.44–0.96), while those aged ≥65 were more likely (ARR=1.54; 95% CI=1.25–1.90). No significant age-related differences were observed in tumor stage, time to surgery, surgical route or approach, or lymphadenectomy. Among patients with aggressive histologic subtypes (n=287), there were no statistically significant differences in receipt of adjuvant treatment for women aged 18-49 (ARR=0.84, 95% CI=0.58-1.21) or women aged >65 (ARR=0.92, 95% CI=0.78-1.08) relative to women aged 50-64 at diagnosis. Conclusion: In the MHS, age-related differences in tumor histology were noted, with older women having a higher likelihood and younger women having a lower likelihood of aggressive and high-risk subtypes than middle-aged women. Despite the age differences in clinicopathology, there were no age-related differences in surgical management of tumors when adjusted for patient and tumor features. Additionally, for those with high-risk tumors, there did not appear to be overall differences in receipt of adjuvant therapy. These findings highlight the possible role of access to care in achieving similar care patterns for women with endometrial cancers regardless of age at diagnosis.