How old is a skunked beer?

Skunky beerAge is not the critical factor. Beer can go "skunky" almost immediately if it is exposed to sunlight. The older the beer is, the more likely it is to have been exposed to light.

Skunking is the result of a reaction between the hop compounds in a beer and UV light. When they hops are exposed to UV light, they change and give off a sulfury smell.

Most bottled, canned, and pasteurized beers will last for many months, even years, without any problems if kept in a cool, dark place. Canned beer cannot be skunked. Bottled beers are will go skunky if exposed to too much light. Brews in green glass are more vulnerable to light than those in dark brown bottles as they let in more UV light. Clear bottles let in the most UV light.

So in other Words there is a difference between a skunky "lightstruck" beer and an oxidized old stale beer.