Using current DNA techniques, researchers found they could narrow a person’s age to within nine years.
Experts said the new test, which can work on dried bloodstains that are several years old, could lead to a major breakthrough for crime scene investigators and offer new hope to “cold cases”.
Existing methods rely on teeth, bones or other body parts to establish the age of a suspect.
But scientists at Erasmus University Medical Centre in Rotterdam, the Netherlands have used a characteristic of immune cells, known as T cells which recognise foreign invaders, to calculate an age.
Their study, reported online in the journal Current Biology, says their test provides better results than previous attempts to pinpoint ages through DNA testing.
“We have demonstrated that human age can be estimated from blood with reasonable accuracy using a simple, robust, and sensitive test assay,” said Dr Manfred Kayser, who led the study.
“Our method is applicable in situations where only bloodstains are available, which covers a large proportion of crime cases.
“I wouldn't be surprised if it could be used on historical blood stains that are decades or 100s of years old.”
T cells contain tiny loops of DNA known as “single joint TCR excision circles” or sj TRECS for short.
The scientists said the number of these loops of DNA declines at a constant rate with age.
Dr Kayser said the number of these molecules in a blood sample is counted against a reference gene not affected by age, which allows them to calculate the total amount of DNA in the sample.
"You have a problem because normally your DNA does not change with age," said Dr Kayser.
"What does change is the activity of certain genes over a lifetime, but that is at the RNA level, and crime labs aren't ready for that. So we really had to look for another approach."
The test estimates an age with an error range of approximately nine years.
The study also suggests that the test would be accurate in placing suspects into generational categories spanning over two decades.
Mark Jobling, a geneticist at the University of Leicester told Nature that the "correlation is pretty impressive".
"How useful it will be in practice as a forensic tool remains to be seen, although there will certainly be forensic cases where it will help as an investigative tool," he added.
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