Considering the significance of lifelong learning in advancing active aging in aging societies, the ability to engage in self-directed learning plays a crucial role for adults. There are many self-directed learning (SDL) tools available that measure the SDL abilities of nursing students and healthcare professionals. However, fewer SDL tools specifically designed for middle-aged and older adults have been developed. The purpose of this research was to examine and confirm the factor structure and the internal consistency of the SRSSDL-adult scale, specifically for middle-aged and older adult learners enrolled in senior learning centers. A cross-sectional method was adopted. Both Exploratory Factor Analysis and Confirmatory Factor Analysis were conducted to assess the structural validity of the scale. The internal consistency was determined using the Cronbach's Alpha coefficient. The results indicated that the five factors -- learning needs assessment skills, learning planning skills, learning execution skills, self-assessment skills, and interpersonal skills -- showed acceptable levels of reliability. The revised 25-item SRSSDL-adult scale was found to be a valid measure of middle-aged and older adults' self-directed learning abilities in the context of senior education programs. The findings of this study have the potential to be utilized by educational institutions and educators involved in senior education programs.