Forest aging limits future carbon sink in China. A study using a process-based ecosystem model with explicit forest age cohorts estimates China's terrestrial carbon sink in the 2010s as 198 ± 54 Tg C yr⁻¹, mainly from middle-aged forests. However, future carbon sink will be limited due to forest aging and slowing atmospheric CO₂ growth. The study emphasizes the importance of considering forest age dynamics in policy-making to achieve carbon neutrality. China's forest area has increased significantly since the 1960s due to large-scale ecological restoration projects. However, the aging of forests will reduce their carbon sequestration capacity, limiting future carbon sink. Future re/afforestation could enhance carbon sink by increasing forest area and rejuvenating forest demography. The study highlights the limited future carbon sink due to forest aging, implying that China's carbon neutrality should not rely solely on ecosystem carbon sink. The study also shows that the carbon sink in existing forests will decrease by -1.1 to -0.35 Tg C yr⁻¹ by 2100. The results suggest that future afforestation and forest management could help maintain the carbon sink. The study underscores the importance of forest age dynamics in carbon sink estimation and highlights the need for accurate data and models to predict future carbon sink. The study also notes that non-forest ecosystems may transition from carbon sinks to sources, further impacting the overall carbon sink. The study concludes that forest age dynamics are crucial for accurate carbon sink predictions and that future forest management should consider these dynamics to achieve carbon neutrality.Forest aging limits future carbon sink in China. A study using a process-based ecosystem model with explicit forest age cohorts estimates China's terrestrial carbon sink in the 2010s as 198 ± 54 Tg C yr⁻¹, mainly from middle-aged forests. However, future carbon sink will be limited due to forest aging and slowing atmospheric CO₂ growth. The study emphasizes the importance of considering forest age dynamics in policy-making to achieve carbon neutrality. China's forest area has increased significantly since the 1960s due to large-scale ecological restoration projects. However, the aging of forests will reduce their carbon sequestration capacity, limiting future carbon sink. Future re/afforestation could enhance carbon sink by increasing forest area and rejuvenating forest demography. The study highlights the limited future carbon sink due to forest aging, implying that China's carbon neutrality should not rely solely on ecosystem carbon sink. The study also shows that the carbon sink in existing forests will decrease by -1.1 to -0.35 Tg C yr⁻¹ by 2100. The results suggest that future afforestation and forest management could help maintain the carbon sink. The study underscores the importance of forest age dynamics in carbon sink estimation and highlights the need for accurate data and models to predict future carbon sink. The study also notes that non-forest ecosystems may transition from carbon sinks to sources, further impacting the overall carbon sink. The study concludes that forest age dynamics are crucial for accurate carbon sink predictions and that future forest management should consider these dynamics to achieve carbon neutrality.