Purpose: The study examined age-contingent effects of organizational capabilities on Sustainable Entrepreneurship among small and medium-sized businesses (SMEs). In particular, it examined how adaptive capability and strategic agility influence SE and how SME age plays a mediating role in this relationship. Design/ Methodology: The study used a cross-sectional survey research approach and was based on the Resource-Based View and Dynamic Capabilities Theory. Using Taro Yamane's formula, a sample size of 382 was calculated from the population of 8,395 registered SMEs in Lagos State; 349 valid responses were examined through a structured questionnaire. AMOS 23 was used for structural equation modeling (SEM) analysis. Four theories were raised and tested. Findings: The results showed that both strategic agility and adaptive capability significantly influence SE, and their combined impact enhances sustainable entrepreneurship. Significantly, the association between organizational capabilities and SE was partially mediated by SME age, suggesting that firm maturity influences how organisational capability transfer into sustainable outcomes. Originality/Value: By questioning the implicit presumption that organizational capabilities are consistently advantageous across enterprises, this study enhances the theory of sustainable entrepreneurship. The study presents an age-contingent capability paradigm that clarifies when and how strategic agility and adaptive capability produce sustainable results by rethinking SME age as a temporal translation mechanism rather than a demographic control variable. The study shows that capability effectiveness is path-dependent and influenced by firm maturity by integrating the Resource-Based View and Dynamic Capabilities Theory through a temporal lens. This reinterpretation creates new opportunities for lifecycle-based capabilities research and offers a process-oriented explanation of sustainable entrepreneurship.