The growth of the older adult population has made attention to the environmental quality of nursing homes an important concern in interior architecture. Despite the provision of basic facilities and safety requirements, many nursing homes have not yet become legible, calming, empowering environments that support older adults’ agency. Accordingly, this study aimed to explain the interior architectural components of nursing homes based on environmental affordances and the environmental press–competence model. It addressed the question of which architectural components can provide genuine opportunities for movement, choice, interaction, control, and the preservation of older adults’ dignity. The novelty of the study lies in proposing an affordance-based framework that links spatial characteristics, individual competence, and older adults’ agency. The research employed a multiple-case study strategy and a qualitative-priority mixed-methods approach across six nursing homes in Tehran. In the qualitative phase, data were collected through observations and semi-structured interviews with six older adults and analyzed using the constant comparative method. In the quantitative phase, 235 questionnaires were completed by staff members and the children or primary companions of older residents. The data were analyzed using descriptive statistics, Cronbach’s alpha, exploratory factor analysis, comparative tests, correlation analysis, and multiple regression. The findings identified six components: perceptual–cognitive, motor–physical, interactive–social, autonomy and control, identity–meaning, and sensory–calming affordances. The overall level of environmental affordances was moderate, while autonomy and control received the lowest evaluation. The results indicate that the quality of nursing homes cannot be achieved solely through safety measures and physical facilities; rather, it requires an affordance-based, agency-oriented, and dignity-centered approach.