This study investigates the impact of a sustainable mindset on psychological well-being and stress levels among 736 Portuguese students from secondary schools and universities. Using validated psychometric instruments, the research examines relationships between well-being, stress, optimism, age, sex, and mindset orientations (Growth Mindset and Fixed Mindset). Findings indicate that higher psychological well-being is significantly associated with a Growth Mindset, correlating with better mental health and lower stress levels. In contrast, a Fixed Mindset is linked to lower well-being and higher stress. Gender differences were noted, with females exhibiting higher Growth Mindset scores and males showing higher Fixed Mindset scores. Multiple regression analyses reveal that well-being and age are strong predictors of mindset orientations for both genders. This study underscores the importance of developing youth policies focused on enhancing well-being and managing stress to promote adaptive mindsets and sustainable attitudes. Such initiatives could foster resilience and positive behavioral changes necessary for long-term sustainability in educational settings. The results provide a foundation for future research and practical applications aimed at integrating psychological sustainability into educational practices.