<p>Although biochar has gained global attention in environmental, agricultural, and geo-environmental engineering applications, its long-term performance, particularly the effects of biochar aging on soil properties, remains poorly understood. To address this gap, this review systematically explores the natural forces that may age biochar and their impact on its physicochemical properties. The potential implications of biochar aging on the engineering properties of biochar-amended soils (BAS) are summarized, considering various influencing factors such as aging methods and soil textures. Different artificial aging methods, including physical, chemical, and biological aging techniques, are reviewed as accelerated proxies for natural biochar aging. The relationships among these methods are established through three quantitative models based on different usage scenarios. To advance the application of biochar in geo-environmental engineering, it is essential to conduct artificial aging tests that more accurately simulate field conditions while thoroughly evaluating the environmental benefits and risks associated with biochar.</p>