Predicting human phenotypes from genotypes is a newly emerging field with relevance for personalized medicine  and forensics . However, only a few phenotypic traits can currently be identified from DNA information with accuracies sufficient for practical applications , most notably human eye (iris) color . It could be expected that individual age is too biologically complex to allow a simple and accurate molecular estimation from biological materials. Indeed, previously proposed genetic methods for human age estimation, based on the accumulation of mitochondrial DNA deletions or on telomere shortening, show low accuracies and various technical problems, and are therefore not suitable for practical applications . Proposed biochemical methods, such as those based on the accumulation of D-aspartic acid, involve the destructive analysis of specific body parts (such as bones, teeth and ligaments), and suffer from technical issues and bio-degradation . In the present study, we demonstrate that human individual age can be estimated accurately and reliably from blood using T-cell DNA rearrangements, and we provide a robust and sensitive real-time quantitative PCR protocol for application in various areas of bioscience.