Rural China's demographic structure is ageing at a rate far exceeding national averages, posing serious challenges to sustainable agricultural production. As a top global producer and carbon emitter, China must ensure food security while reducing agricultural emissions. However, current understanding of these dynamics remains limited. This study establishes the year 2000 as the benchmark for when rural ageing began in China. Through analysis of data from over 1,400 surveyed Chinese counties through 2020, we examine related trends. Findings show ageing correlated with a 10.2% rise in agricultural diesel usage intensity and 13.3% increase in plastic film use, together raising CO2 emissions 7.0%, posing threats to both the environment and arable land. To address these concerns and explore options for achieving sustainable agriculture amid ageing rural populations, we quantitatively assess future impacts and potential mitigation through increased adoption of new family farming models. As simulated, compared with 2020, projections for 2100 indicate that fertilizer, diesel and pesticide use intensities may fall 28-29%, 7-26% and 35-51%, lowering agricultural CO2 emissions by 17-27%. These findings indicate that the scaled and specialized organization and production technologies employed under new family farming models have the potential to help offset the negative impacts associated with ageing rural populations.