I don't know much about this disorder, but what I've read suggests it generally begins in young adulthood. Not to disparage the pscyh testing, but we've been told repeatedly by our psychiatrists that if personality testing is not administered by a very skilled clinician, it can be misinterpreted. I personally would want to rule out all other mental health/neurological disorders before settling on a diagnosis of this sort.
What does your son's psychiatrist think of the diagnosis?