To engage more youth in service, we require further research on the characteristics of youth who serve, particularly disadvantaged youth with limited access to formal service opportunities. This study investigated the positive youth development characteristics of New Zealand youth who decided to mentor younger peers in the Stars program for the first time (n = 109), those who returned to mentor for a subsequent year (n = 48), and similar youth not involved in Stars (n = 51) to determine what characteristics differentiate these groups. Returning mentors had the highest levels of social competency and involvement and a strong leadership orientation. New mentors had the second highest levels of leadership orientation but the lowest levels of social competency and involvement. The propensity for leadership in mentors was associated with having many positive adult role models. Strategies to engage more young people in service as cross-age peer mentors are discussed.