DiverDLE,
Apparently your son fell June 15, 2017, is that correct? If so, and there's was an actual skull fracture, I would be hesitant to allow SCUBA diving for six months after this injury.
I am not a doctor, but do have my MSPH degree, and also experienced a bicycle fall some years ago, with concussion, and subsequent dizziness. I was semiconscious for about 20 minutes after the fall, and do not remember events just prior to the fall, and until I "woke up" in the ER. I stayed away from any water activities for six months, and when I finally went swimming I went up to the lifeguards to tell them of my injury, the dizziness subsequent to that (which ebbed over time) and to ask them to keep an eye on my during that first swim, which they did. I was concerned about flip turns, and whether they would trigger a dizziness episode. They did not, and I had a good swim, then returned to diving, first again in the pool, then in open water.
Concerning your son, you have not described any of his symptoms, but a skull fracture is fairly serious, and takes months to heal fully, not weeks. Hence my thoughts on waiting six months.
SeaRat
PS, the ER doc told me that "...without a helmet, if I had been unlucky that day, I would have lived." The comment "No Helmet?" above is a good one. My helmet did its job, but was handed to me in a sack of helmet pieces.