The learning environment of Universities of the Third Age (U3As) plays an important role in ensuring the quality and effectiveness of older adults’ learning. A systematic literature review reveals the absence of a scale for measuring the learning environment of U3As. The purpose of this study is to design and develop a learning environment scale for U3As in the Internet Age by employing social space theory, connectivism theory, and outcome-based education theory. Both qualitative (interviews with older adults, and Delphi method) and quantitative (internal consistency reliability, exploratory factor analysis, and confirmatory factor analysis) procedures were adopted. As a result, a five-point Likert scale with 78 indicators grouped under eight factors was developed and confirmed, which included institutional support, teacher support, technical support, learning content, learning methods, assessment, learning interaction, and spatiotemporal adaptation. The items showed good validity and reliability with favorable results. This scale is expected to diagnose and improve the learning environment of existing U3As and provide a reference for the sustainable development of U3As.