Background: Women diagnosed with breast cancer may have distinct physical, psychosocial, and survivorship needs that vary by age. Supportive care aids recovery, yet utilization may be influenced by access. We examined age-related differences in supportive care use in the Military Health System, a universal healthcare system. Methods: Using the MilCanEpi database linking Department of Defense cancer registry and medical claims, we identified women aged ≥18 years diagnosed with stage I–IV breast cancer from 1998-2014. Supportive care included physical therapy (PT), occupational therapy (OT), mental health services (MH), and nutritional counseling (NTC). Multivariable logistic regression and trend analyses estimated odds ratios (aORs) and 95% confidence intervals (CIs) for supportive care use by age within the first year post-diagnosis, adjusting for sociodemographic and clinical characteristics. Stratified analyses examined heterogeneity by tumor stage, care setting, and treatment, with effect modification assessed using likelihood ratio tests. Results: Among 13,744 women, 11% were aged 18-39, 24% 40–49, 42% 50–64, and 23% ≥65. Overall, 53% received PT, 19% OT, 10% MH, and 19% NTC. Compared to women aged 18-39, older women had higher odds of PT use (40-49: aOR=1.42, 95% CI=1.22, 1.66; 50-64: aOR=1.58, 95% CI=1.35, 1.84), though the ≥65 group was not significant, with a significant increasing trend by age (aOR=1.18; 95% CI: 1.10, 1.26). Conversely, older women were less likely to receive MH (40–49: aOR=0.80, 95% CI=0.66, 0.99; 50–64: aOR=0.50, 95% CI=0.41, 0.62; ≥65: aOR=0.37, 95% CI=0.15, 0.87), with a significant decreasing trend by age (aOR=0.70; 95% CI: 0.63, 0.77). No age differences were observed for OT or NTC. MH (χ²=10.26, df=3, p=0.017) and NTC (χ²=17.98, df=3, p<0.001) were lower in private-sector care. PT use increased with age only among non-radiation patients and was highest in patients ≥65 who received radiation (χ²=9.00, df=3, p=0.029). Older patients had steeper declines in MH across surgical groups, particularly those with no surgery (χ²=21.45, df=6, p=0.002). Conclusion: Despite minimized financial barriers in the Military Health System, age-based differences persisted: younger women more often received MH and older women PT, while OT and NTC showed no age differences. Differences by care setting, surgery, and radiation highlight the need for tailored, age-sensitive survivorship care and further research on whether age differences reflect needs, preferences, or referrals.