Abstract: OBJECTIVE: To investigate associations of age at type 2 diabetes (T2D) detection with HbA1c. RESEARCH DESIGN AND METHODS: We examined associations of early-onset T2D (age of detection 20-39 years) and age at T2D detection with HbA1c in Veterans with incident T2D (1/1/2008-12/31/2016; n = 851,302). RESULTS: About 3 % (n = 22,649) of men and 11 % (n = 5,117) of women had early-onset T2D. Compared to men with later-onset T2D, men with early-onset T2D had a 0.71 (95 %CI 0.69,0.73) greater HbA1c after detection, a 0.78 (95 %CI 0.77,0.80) greater mean HbA1c, and a 0.05 (95 %CI 0.04,0.05) greater coefficient of variation (CV). Each 10-year decrease in age was associated with greater HbA1c after detection, mean HbA1c, and HbA1c CV (β 0.21 (95 %CI 0.21,0.21), 0.25 (95 %CI 0.24,0.25), 0.02 (95 %CI 0.02,0.02), respectively). In women, early-onset T2D was associated with a 0.14 (95 %CI -0.18,-0.10) lower HbA1c after detection and a 0.01 greater CV (95 %CI 0.01,0.01). Each ten-year decrease in age was associated with greater mean HbA1c and CV (β 0.09 (95 %CI 0.08,0.10); 0.01 (95 %CI 0.01,0.01), respectively). CONCLUSION: Among male Veterans, early-onset T2D was associated with greater HbA1c and greater HbA1c variability. Similar results were seen among women but of lesser magnitude. Longitudinal research examining sex-specific impacts of early-onset T2D on clinical course is needed.