Background: Initial mammography screening age recommendations vary by organization, with the United States Preventive Services Taskforce recommendations beginning at 50 years and the American College of Obstetricians and Gynecologists and the National Comprehensive Cancer Network recommendations beginning at age 40 years. This study aimed to examine the impact of early age recommendation for initiating screening mammography (i.e., 40 years) on time to breast cancer diagnosis. Methods: This is a retrospective cohort study of adult women who received a screening mammogram between 1/1/2012 and 12/31/2022. The outcome of interest was a breast cancer diagnosis (ICD-9 code: 174.X; ICD-10 code: C50.X) any time after the initial screening. Members were stratified by age at the initial mammogram, with on-time mammograms defined as those occurring during the 50^th year of life and early mammograms defined as those occurring in the 40^th year. Survival analysis was conducted between the two groups. Incidence rate differences (IRD) and ratios were calculated between groups for 1-, 3-, 5-, and 10-year follow-up analysis; logistic regression modeling was also performed. All analyses were conducted in Python and R; p < 0.05 was considered significant. Results: In total, 22,843 members were included in the study, with 11,730 (51.4%) having on-time mammograms. On-time screening members were more likely to have unknown socioeconomic status (SES) compared to early screening members (26.4% vs. 24.6%, p = 0.022) and to reside in rural zip codes (42.2% vs. 39.1%, p < 0.001). After 10 years of follow-up, 285 of 2,647 remaining members developed breast cancer (incidence rate 10.77 cases per 1,000 person-years [PY] observed [95% confidence interval (CI) 9.55-12.1 cases per 1,000 PY]). Early mammograms were associated with significantly lower IRD at 3- (IRD: -1.85 cases per 1,000 PY [95% CI -2.76 to -0.93]; p = 0.0001), 5- (IRD: -1.92 cases per 1,000 PY [95% CI -2.86 to -0.97]; p = 0.0001), and 10- (IRD: -7.15 cases per 1,000 PY [95% CI -9.66 to -4.64], p < 0.0001) year follow up periods. Early mammograms were associated with significantly longer time to diagnosis during survival analysis (97.5% diagnosis-free vs. 95.4%, p < 0.0001). Controlling for SES, early mammograms were associated with significantly lower hazard for breast cancer diagnosis at any time (hazard ratio [HR]: 0.62 [95% CI 0.48-0.78], p < 0.0001). Unknown SES was also associated with significantly lower hazard compared to those with medium SES (HR: 0.47 [95% CI 0.33-0.67], p < 0.0001); however, no other SES categories demonstrated significant differences. Conclusions: The primary goal of breast cancer screening is to reduce breast cancer incidence and mortality. In this study, early mammography at age 40 years was associated with significantly lower incidence rates after 3-, 5, and 10-year follow-ups. Additional studies on the impact of early mammography and breast cancer mortality in this population are warranted.