Lifespan developmental theories and research suggest a positive effect of adult age on prosociality. However, this effect lacks consistency, with many studies excluding the period of midlife. This study summarized cross-sectional studies on adult age and prosociality, combining 120 (independent) samples (n = 103,829) in a lifespan meta-analysis approach. Linear and quadratic age effects on prosociality were analyzed, as well as comparisons between younger, middle-aged, and older adults. Prosociality was assessed via behavioral measures and self-reports. In both these domains, results indicated small linear age effects and higher prosociality in older compared to younger adults, supporting the hypothesis of increased prosociality in older age. Additionally, leveraging open data sets (64/120 independent samples), predominantly unpublished, we found some evidence for potential quadratic age effects on behavioral prosociality: Middle-aged adults exhibited higher behavioral and self-reported prosociality than younger adults, but no differences between middle-aged and older adults were observed. This meta-analysis offers new perspectives on age trajectories of prosociality, suggesting midlife as a potentially important phase of pronounced prosociality.