Ageing of badgers is something of an acquired skill and is often based upon craniometric (i.e. skull) measurements. A paper in 1993 by biologists at the University College in Dublin suggests, however, that such measurements have insufficient reliability to accurately age badgers more than three years old, when skull growth is complete. Instead, the scientists recommend that, for adult badgers, counting cementum annuli in teeth, the dental equivalent to counting the rings of a tree stump, is a more reliable method. Unfortunately, this generally requires a dead badger and may not be universally applicable because annuli deposition is can vary geographically. This technique has proved quite successful for ageing badgers in Sweden, for example, but appears far less reliable for ageing individuals from the southwest of England.
In the wild, few badgers appear to survive more than six years, although there are exceptions. In Badgers, Neal and Cheeseman describe a male cub that Chris Ferris watched regularly that reached 11.5 years old before being killed by diggers and a female tagged in Woodchester Park in Gloucestershire who lived for 14 years. The authors consider it very rare for badgers to exceed 10 years old, although the occasional animal may make 15. A study of 21 social groups at Woodchester Park between 1985 and 1993, published by Lucy Rogers and colleagues in the Journal of Zoology, revealed that females typically lived longer than males and that about 80% of the population was composed of badger four years old or younger.
In his 2005 compendium Longevity of Mammals in Captivity, Richard Weigl lists six captive badgers that survived into their teens, with the oldest being a male that died at Praha Zoo in the Czech Republic during December 1979 at 18 years and 7 months old. Neal and Cheeseman cite an animal kept in captivity by Ruth Murray that reached 19.5 years old, the oldest record I have found to-date.