I know lot’s of kids do this but is he showing other signs of undersuppression?  My son is late onset and when he first started having symptoms - perspiration odor and acne - he was waking up with erections and showing alot of interest down there.  He was almost 8 at the time.  Now that he’s being treated, he’s going to be 11 and he really hasn’t shown any interest in doing this in years.  So it could be normal or possibly a symptom of high testosterone which I think was the case with my son.  The doctor also told me to watch for erections when he was first diagnosed as a sign of early puberty.