University mentoring programs are often implemented as an instrument to support students' personal development and successful transition to university. Scholars and practitioners alike emphasize the importance of matching for high-quality peer mentoring. However, mentoring theory and research lacks specificity regarding relevant characteristics and type of fit, as well as predictive power, as fit between mentors and protégés is often conceptualized as subjective perception of a conglomerate of various characteristics. In the present study, we address these issues by examining the extent to which deep-level similarity between mentors' and protégés' personal values (i.e. conservation, self-transcendence, openness to change, self-enhancement) predicts high-quality mentoring relationships in terms of protégés' learning and growth and willingness to mentor 12 months later through role modeling. We tested the proposed mediation model in a prospective three-wave field study, using polynomial regression analyses and response surface analysis in a sample of 149 mentor-protégé dyads in a formal peer mentoring program at a German university. Results show that the impact of deep-level value congruence on the mentoring process varied depending on the value dimension, revealing self-enhancement as a key dimension. In this regard, deep-level congruence in self-enhancement values -- independently rated prior to the mentoring relationship -- positively predicted protégé's learning and growth and willingness to mentor in the future through role modeling support. The implications of these findings, especially for the matching process, are discussed.