The idea that dogs age seven years for every one human year is a myth, scientists have claimed..

University of California researchers say they have also found puppies are middle-aged by the time they are two, although dogs tend to age more slowly than humans in later life.

By the time they get to three - and are possibly still getting away with things due to being considered young - dogs are closer in age to a 50-year-old human, according to the university's research.

The study looked at how dogs aged by focusing on the DNA methylation in 104 labradors aged between four weeks and 16 years.

The DNA contains marks that change over time as a cell matures, allowing scientists to track the animal's biological age.

After assessing the dogs' results, the researchers then compared their findings to those from 300 humans.

By the age of two, the Labrador DNA was equivalent to a human in their early 40s, rather than the 14-year-old, which the traditional formula would suggest.

However, ageing slows in dogs over time, meaning that by the age of 10, a Labrador is similar to a person aged 68.

This ties in with the long-held formula for calculating the age of dogs, which was developed on the assumption that most canines lived until around 10, while humans lived until around 70.

"The expected lifespan of Labrador retrievers, 12 years, correctly translated to the worldwide lifetime expectancy of humans, 70 years," the researchers said.

But lest anyone thinks this research makes puppies any less lovable, the scientists also observed that there were similarities in the ageing process, whereby eight-week-old puppies resembled nine-month-old babies.