The birthday candles in your veins

Ewen Callaway writes in Nature:

A drop of blood can provide a rough estimate of a person’s age, helping forensic investigators to draw physical profiles of suspects and victims who leave few other traces behind.

Conventional forensic DNA analysis matches samples gathered from crime scenes and compares them with those of people identified in an investigation or in a database. Increasingly, however, investigators are building physical profiles of individuals on the basis of their DNA alone. For instance, six genetic markers can indicate whether a person has blue or brown eyes.