There could be many reasons:
Most of the young people like to drink. They want to experiment in life.
people drink milk when they are young to have healthy bones or when they just want to
it depends on what you mean by young, for people who can legally drink, if they drink they drink anywhere they can get a drink. for under age people, they usually drink at places that they can get a drink without getting in trouble. this could be a friend's house, at an abandoned area, or even at home when an adult is not there, or not paying attention.
beer
Lots of people in Ireland drink Jameson's. As it is a whiskey, it tends to be a drink that older people drink, so not as many young people drink it as older ones do.
Most teens succumb to peer pressure by their friends.
Seriously? Of Course!
so they don't over heat
People have always been drinking milk. The young drink the milk of their mothers to survive.
Young wombat joeys need to drink milk from their mother.
Kids at young age drink because they think it's cool and that they could showoff that's why they drink
If trends and studies in the UK, and college culture in the US are any indication, then the answer is young people, usually in their first year away from home.