A teenager, or teen, is a person who falls within the ages of 13 to 19 years old. Whereas preeteenager or tweenager is that stage of human development which follows early childhood and preceding adolescence. The word "teenager" is another word for an adolescent. When a teenager turns 20, they are no longer a teenager: they are no longer in that developmental stage. Now this may seem like a problem to most of the parents; an end to development after a certain age. But trust me it’s not. Setting some things in motion, at the right time can your child’s personality and eventually their life.