>>Since when is an 18 year old a teen?<<
By definition, anyone between the ages of thirTEEN and nineTEEN is a teenager.
I think that it is safe to say that the article is using the teen reference to drum up sympathy for Mr. Johnson and to give the impression that he shouldn’t be held responsible for his actions considering his “tender age.”
If you will notice he is still in high school, when he should have graduated last June. Then please take notice the blurb on his high school, which is obviously a continuation school or reform school.
I am willing to bet that this isn’t Mr. Johnson first encounter with the police department.