I agree, but you seemed to be missing the point of the article. The article was not prostitution is bad, it is look at these people profiting of the abuse of children, people who had every reason to believe abuse was occurring but who turned the other way and allowed it to happen as they were making money. So your comments seems to be ignoring the article entitling and instead picking a different battle, a battle that was not bring waged.
If the same girl was 21 I would say it's absolutely ok.