can we sue a student over 18?

Anybody can sue anybody for anything, but that doesn't mean that your friend's claim will succeed.  From the little you've written, I don't see a claim unless your friend had some basis where he was entitled to rely on the student's advice.  If some random acquaintance gives you a stock tip, you can't hold him liable if the stock goes down (unless he knew he was lying when he gave you the tip). Did your friend pay the student for his advice?  Did the student hold himself out as some sort of expert in the subject area (for example, was he employed in the financial aid office giving advice about how to apply for aid?)  Was he a professional (doctor, lawyer, etc.) whom your friend paid for professional advice, and the advice was so deficient that he committed malpractice?  Did the student deliberately mislead your friend?  Absent any of these circumstances, I don't think your friend  has a case.