Introduction: Aging is often associated with low-grade chronic inflammation and a senescent immune system. Vitamin D is a regulator of immune function, and low plasma vitamin D is associated with poor health. The association between plasma vitamin D and inflammatory biomarkers and risk of postoperative complications and survival in patients with colorectal cancer (CRC) is unknown. Our aim was to investigate these associations and how they are influenced by age. Materials and methods: Circulating vitamin D and the inflammatory biomarkers C-reactive protein (CRP), interleukin (IL)-6, and YKL-40 were measured in 398 patients with stage I–III CRC preoperatively. Older patients (≥70 years, n = 208) were compared to younger patients (<70 years, n = 190). The relation between vitamin D and complications and high inflammatory biomarker levels was presented by odds ratios ([OR], 95% confidence interval [CI]). Associations with survival were presented with hazard ratios ([HR], 95% CI). Results: Plasma vitamin D was higher in older patients than in younger patients (75 vs. 67 nmol/L, P = 0.001). High vitamin D was associated with low plasma CRP in younger patients (OR = 0.35, 95% CI 0.17–0.76), but not in older patients (OR = 0.93, 0.49–1.76). High vitamin D in older patients with CRC was associated with reduced risk of major complications (OR = 0.52, 0.28–0.95). This was not found in younger patients (OR = 1.47, 0.70–3.11). Deficient vitamin D (<25 nmol/L) was associated with short overall survival compared to sufficient (>50 nmol/L) irrespective of age (HR = 3.39, 1.27–9.37, P = 0.02). Conclusion: For patients with localized CRC, high vitamin D levels before resection were associated with reduced risk of high inflammatory biomarkers for younger patients and reduced risk of major postoperative complications for older patients. Vitamin D deficiency was associated with reduced survival regardless of age.