A teenager (or teen for short) refers to someone older than 12 and younger than 20. Generally these are people moving from childhood into adult responsibilities. Teens are often still living with older family; although some teens have moved out and may be starting their own, young families. The amount of independence that a teenager has will vary widely in different cultures and parts of the world.
Teens are developing their identity. As part of this, they may play around with various decorating schemes and furnishings. Some of the things they try seem a bit extreme -- testing boundaries. Social relationships are also a key part of teen life. So it's good to have a place to invite friends to "hang out".
Teenagers often have much more school work and need a place to study, to read and prepare their homework assignments. A comfortable reading chair, desk or table, good lighting, and a place to keep office supplies may be useful.
Toward the end of teen years, some teens move out of their parents' home to live on their own, forming a new family or with other young adults -- sometimes in a college dorm. Money tends to be tight, but obligations also tend to be light.