The decline of signal joint T-cell receptor rearrangement excision circles (sjTRECs) in human peripheral blood has been demonstrated to be age-related, which can be a potential marker for individual age determination. However, little is known about the quantitative relationship between the levels of sjTREC and age. The aim of the present study was to investigate the levels of sjTREC in peripheral blood leukocytes (PBLs) among different age groups in Chinese population, so as to clarify whether it could serve as a suitable marker for biological age estimation in forensic practice. sjTREC levels were measured by real-time quantitative PCR analysis in peripheral blood samples from individuals of known age (n = 248). The quantification results showed that sjTREC declined in human PBLs in an age-dependent manner (r = -0.8177, P < 0.01). The formula for age estimation based on peripheral sjTREC decline was Y = -24.921x - 39.932 ± 10.47 (Y age, year; X log sjTREC/TBP; 10.47: standard error). Furthermore, there was no difference between males and females with regard to sjTREC levels. These results suggest that assessment of sjTREC in PBLs might be a valuable additional tool in age determination, especially in cases where traditional morphologic information is absent or inefficient in forensic practice.