The simple answer is yes, the beer is still good insofar as it is safe to drink. (Typically, the drink-by dates on beers are four to six months out; this is based on how long the brewer thinks the beer can retain fresh flavor.)
Children and young people are advised not to drink alcohol before the age of 18. Alcohol use during the teenage years is related to a wide range of health and social problems. However, if children do drink alcohol underage, it should not be until they are at least 15.