Mobilizing older environmental volunteers presents a promising strategy for addressing two global challenges: the environmental crisis and population aging. However, research specifically focused on older adults in the context of environmental volunteerism remains extremely limited, despite notable age-related and field-specific motivational patterns that warrant focused investigation. This study explored the motivations of older adults engaged in environmental volunteerism through semi-structured interviews with 54 older environmental activists. Thematic analysis was used to identify and examine motivational themes and patterns. Five overarching themes emerged: 1) A problem-solving orientation involving becoming aware of environmental issues—such as recognizing their severity and urgency and noticing specific environment-related changes—and spreading this awareness, 2) Lifespan developmental needs, including generativity and a commitment to ensuring human and planetary survival, 3) Immediate personal considerations, such as knowledge acquisition, social connection, and the continuation of past interests, 4) Beliefs and value systems, 5) Emotions and emotion regulation. Additional findings on motivational features include: appreciation for cumulative progress and long-term continuity; valuing opportunities to gain knowledge and master new skills—including those not pursued earlier in life; and emphasizing the quality rather than quantity of social relationships, with less reliance on activism as a remedy for loneliness. Future research should examine how nature contact and connectedness function as emotional regulation strategies, and investigate motivational differences across volunteer programs, modalities, and intensity levels. This study offers foundational insights into older adults’ motivations for environmental activism, informing future research and offering immediate implications for policymakers and organizations designing programs to recruit and retain older environmental volunteers.