The world's ageing population presents both challenges and new opportunities for urban design, particularly in high-density cities like Hong Kong. This study investigates intergenerational cooperation in the co-design of urban public spaces, assisted by Virtual Reality (VR) environments. Through a series of workshops inviting youth, university students, middle-aged adults, and older residents to work in small teams, we documented their interactive behaviours and observed how the involvement of different age groups may influence the cooperative process and design outcomes, especially when VR tools were involved. Our findings shed light on several key aspects. First, how work engagement levels differ based on highly-, moderately-, and non- intergenerational groups. Second, observable patterns of common task-role distribution between age groups within a self-organised collaborative process. Thirdly, the various types of social participation, from cooperative, associative to solitary, emerged as a consequence of such interactions. Finally, from the co-created public space designs, any transformational and transactional values that arise were discussed. The study contributes to ways in facilitating more age-friendly approaches in urban design, especially in face of digital transition, and highlights the importance of intergenerational cooperation in design processes so as to create more inclusive environments.