Objectives: To determine the relationship between age, hamstring tightness, trunk flexibility, and lumbar lordosis angle (LLA), and examine how these variables relate independently of age. Furthermore, we identified the most significant predictor of LLA in sedentary adult females with hamstring tightness. Methods: This cross-sectional study included 80 sedentary adult females (20-59 years old) with hamstring tightness, which was assessed using the active knee extension (AKE) and straight leg raising (SLR) tests with a universal goniometer. Trunk flexibility was assessed using the fingertip-to-floor test, and the LLA was evaluated non-radiographically using a flexicurve (flexible ruler). Results: A significant correlation was observed between age and all examined variables (p < 0.001). Specifically, age was associated with increased fingertip-to-floor distance, suggesting reduced trunk flexibility (β = 0.756), and increased SLR (β = 0.517) and AKE (β = 0.424) angles, indicating increased hamstring tightness. Furthermore, age was the significant independent predictor (p < 0.001) of LLA. Conclusions: Age is significantly correlated with decreased flexibility and reduced lumbar lordosis angle in adult females. Among the variables examined, age was the significant independent predictor of LLA. These findings highlight the need for early detection and management of age-related musculoskeletal alterations to maintain proper spinal alignment and functional mobility.