Background: Right-sided aortic arch with Kommerell diverticulum (RAA-KD) has complex three-dimensional anatomy. Methods: We retrospectively analyzed computed tomography angiography data from 65 adults with RAA-KD using centerline-based reconstruction. Patients were stratified by conventional maximal KD diameter (D_KDmax) into <55 mm (n = 38) and ≥55 mm (n = 27) groups. Age associations, adjusted group differences, and continuous associations with centerline-derived KD diameter at maximal cross-sectional area (D₁₀) were examined. Results: After sex adjustment and false-discovery-rate correction, all aortic diameters increased with age; the ascending aorta, arch, and descending thoracic aorta also elongated, whereas aortic isthmus (L₄) and KD (L₅) lengths were not age-associated. After age and sex adjustment and false-discovery-rate correction, diameters of the ascending aorta, aortic arch, and descending thoracic aorta (D₂–D₈), as well as KD-related diameters (D₉–D₁₂), remained larger in the ≥55 mm group; L4 was shorter and L5 longer. In continuous models, D₁₀ was positively associated with all non-KD diameters, most strongly with the adjacent proximal descending aorta (D₇), and independently associated with shorter L₄ (B = −0.548; 95% CI, −0.828 to −0.268) and longer L₅ (B = 0.639; 95% CI, 0.412–0.866; both p < 0.001). Conclusions: RAA-KD demonstrates generalized age-associated thoracic aortic enlargement and localized KD-associated remodeling. Comprehensive three-dimensional assessment may inform evaluation of the adjacent aorta and proximal sealing zone for thoracic endovascular aortic repair.