I think there is a huge difference between a question that can only be answered with speculative/purely subjective answers, and a question that you can only answer with speculative/purely subjective answer (and by "you", I don't mean only the OP!).
I believe that one of the interesting points of Academia.SE is to try to bring more facts to questions for which you sometimes only have an intuitive idea, which means that when you ask a question, you might not know whether there is an objective answer or not. Of course, as eykanal pointed out, some questions are obviously rants or only explicitly asking for opinions, and such questions should be closed.
I would say that the question you mention does not belong to such categories: perhaps there exists some official numbers that can help. For instance, if the following question would have been asked: "I received an application from a French student with a score of 14.5/20 at the Baccalauréat, série scientifique, how do I evaluate that?", I could objectively answer that the Série Scientifique is usually considered in France as the most selective category, that around 80% of the students have the baccalauréat, and among this 80%, only 28% have a 14 or more, which is given by a Mention Bien or Très Bien. So 14.5 is a good score.
When it's not obvious, I would say that the best is to let the question lives, and monitor the answers and comments: if there are too many subjective/speculative answers, then it might be worth closing the question. Note that it's quite frequent that some answers are just transformed into comments.
Globally, my point is: don't ask to close a question just because you can't answer it. The objective is to let the community work (I think we had a really nice example of a question closed, edited, reopened, without mod intervention, that's what we should be aiming for), so be involved in the community by asking questions and providing answers, if you can't vote, then leave comments, bring it to Meta, it might attract the attention of high-rep users.
There is a reason for the need of 5 close votes from users who have enough reputations, it's to reach some notion of consensus from users who been involved enough in the community.