Age is directly linked to changes in DNA methylation. 

During the course of life, biochemical changes to the DNA are induced by a combination of environmental influences, aging-related processes, and certain lifestyle factors such as diet and smoking. One of the changes is DNA methylation, a process that involves the addition of methyl groups to specific DNA segments, without altering the DNA sequence. 

Although the exact mechanisms that cause age-related DNA methylation changes are not yet fully understood, DNA methylation is currently the most promising molecular marker for monitoring aging and developing age predictors.