This chapter examines the integration of positive psychology (PosPsy) into second language (L2) teaching and learning across the lifespan, emphasizing its potential to enhance motivation, resilience, and well-being in language learners. Language acquisition is a lifelong endeavor, shaped by cognitive, social-emotional, and developmental changes that vary across childhood, adolescence, adulthood, and old age. This chapter explores individual differences in L2 learning at each developmental stage, drawing on relevant theories and research to highlight the unique characteristics and needs of learners. It discusses how developmental factors influence L2 acquisition and presents developmentally appropriate teaching strategies and interventions tailored to these differences. By applying PosPsy principles, such as fostering positive emotions, strengths, and supportive learning environments, this chapter provides a framework for promoting effective and enjoyable L2 learning at every life stage. Key questions addressed include the role of individual differences, the insights provided by research on stage-specific L2 learning, and the application of PosPsy to support positive outcomes in learners of different ages. The goal is to gain a deeper understanding of lifespan-related factors in L2 education and practical strategies to enhance learner experiences through the lens of positive psychology.