Aims Forest productivity may decrease with increasing stand age, which may be related to a shift in the nitrogen (N) and phosphorus (P) nutrient balance. However, it is unclear how the plantation nutrient balance changes with stand age and how it affects plantation productivity. Methods We experimented with increasing stand ages (6-, 10-, 15-, 25-, 30-, and 34-year-old stands) in Castanopsis hystrix plantations in southern China. Plant growth and the carbon (C), N, and P dynamics were assessed at the ecosystem level (leaf–litter–soil–microorganism). Results Increasing stand ages reduced plantation productivity and leaf N:P ratios (lower leaf N concentrations and stable leaf P concentrations). The reduced productivity may be related to increased N consumption rather than possible P limitations. Increasing stand ages increased N consumption mainly through decreasing soil NO ₃ ⁻-N concentrations and microbial biomass without altering plant N resorption, although enhanced N-acetylglucosaminidase, cellobiohydrolase, and polyphenol oxidase activity might accelerate N mineralization. Increased soil total P concentrations and microbial biomass P rather than plant P resorption would support a larger P supply for plants with increasing stand ages. Conclusions These results suggest that increasing stand ages can contribute to N consumption rather than elevate possible P limitations. Therefore, N fertilizer management should receive attention to maintain the productivity of C. hystrix plantations with increasing stand age.