I think most of the disagreement in this thread comes from when is someone no longer considered a child.
According to the applicable laws, anyone under 18 is still a child, and needs to be treated as such.
Most people in the thread are arguing that 18 is to high of an age for this, while others are arguing that it is the proper age.
I personally believe that setting this age at 18 detrimentally affect those youth, who will become adults who are less individualistic and less capable. I may or may not be wrong about this. Read reificators comment for a better phrasing of this.
Those who believe that this is the proper age believe that this is protecting those youth and allowing them to grow into the adults they have potential to become. They may or may not be wrong about this.