Can a 18 year old boy have a long distance relationship with a 13 year old girl?

This is a terrible idea.  As soon as this relationship becomes sexual in nature, he is breaking the law.  That means if either of them undress on camera, discuss sexual matters in a sexual way.  Suffice to say, an 18 year old has no business with anyone under the age of 16 (the age of consent).  I don't even understand what an 18 year old could possibly have in common with a middle schooler.  Not to put too fine a point on this, but if your "friend" wants to avoid trouble they will break off the "relationship" immediately.  Again, at 18, your friend should be going to work or to college and the 13 year old has not even gone through puberty.  Its just plain WRONG