What Does it Mean When an Adult Has "The Mind of a Teen"?

I really hope the police find the woman from the area who has gone missing. What I have wondered about is the description of her as having the mind of a teen. What does that mean, exactly? When I was a teen, I was basically a freshman in high school. I was with my friends when we walked around and THEY made some bad decisions, like stealing hood ornaments off cars. I thought it was kind of goofy and irresponsible, and I suppose I was guilty by association, but that's the extent to which we were incapable of appropriate decision-making.