<p>Climate influences diseases, and biological age serves as an overall health index. However, research linking climate to biological age is limited. This study investigates associations between extreme temperature, relative humidity, and biological aging. We analyzed participants (<i>n</i> = 7,430) from the China Health and Retirement Longitudinal Study (CHARLS). Biological age was measured using a simplified version of AnthropoAge (S-AnthropoAge). The age gap, the difference between chronological age and S-AnthropoAge, indicates accelerated aging if greater than zero. Extreme climate was defined by percentiles: 5th and 95th for temperature, 10th and 90th for humidity. Linear mixed models assessed the relationship between extreme climate days and biological aging, with stratified and sensitivity analyses for robustness. Compared to the lowest quartile, the age gap changed by 1.079 years (0.711, 1.446) for temperatures above the 95th percentile, -1.888 years (-2.302, -1.474) for below the 5th percentile, -0.881 years (-1.207, -0.555) for humidity above the 90th, and 0.473 years (0.111, 0.835) for below the 10th. For combined conditions, the age gap changed by -1.440 years (-1.778, -1.103) for high temperature and humidity, 0.678 years (0.424, 0.933) for high temperature and low humidity, and − 1.122 years (-1.485, -0.759) for low temperature and low humidity. The study found a significant association between extreme climate and biological aging. High temperatures and low humidity were associated with accelerated aging, while low temperatures and high humidity were linked to deceleration. High temperature and low humidity combination was associated with accelerated biological aging, while other combinations appeared to correspond with deceleration.</p>