Against the backdrop of China’s shifting labor force, the “35-year-old threshold” in recruitment has become a pressing labor market issue. From the 1990s to 2010s, China’s population aged 60 and above increased from 8.6% to 13.3%, while the peak income age declined from 55 to 35, creating a stark contradiction between population aging and income peak rejuvenation. Despite its prevalence, academic research on the causes and impact of age discrimination on firm productivity remains limited.

This paper leverages tens of millions of job descriptions from a major Chinese online recruitment platform in 2021 to construct a city-level age discrimination index using machine learning models. Baseline regression results show that a 1% increase in age discrimination reduces labor productivity by 0.082%, TFP by 0.114%—0.119%, and human capital investment by 0.220%—0.233%. Mechanism testing reveals that emerging technology skills and creative skills significantly increase the probability of age restrictions, while traditional skills correlate with higher age acceptance. Regression discontinuity analysis shows a significant negative discontinuity at age 35 in technology-intensive sectors with rapid skill iteration, but no significant discontinuity in traditional manufacturing and labor-intensive services where experience holds greater value. Heterogeneity analysis indicates that technology-intensive firms suffer the greatest productivity decline and wage reduction, while labor-intensive and capital-intensive firms primarily experience a wage effect with a minimal productivity impact. Through the analysis of corporate annual report texts, it is found that age discrimination significantly reduces both experience capital dependency and human capital cultivation intensity, indicating that the decline in the utilization of experience capital and the reduction in human capital investment jointly explain why age discrimination impairs firm productivity. Finally, a better business environment can mitigate the above negative impact of age discrimination through enhanced market efficiency and institutional constraints.

The main contributions of this paper are as follows: It reveals the formation mechanism of age discrimination from the demand size and its impact on productivity efficiency, and constructs a novel city-level discrimination index based on tens of millions of job descriptions, providing empirical evidence on the impact on efficiency and costs, and offering policy insights for employment equity and resource optimization.