Waiting depending on how close the teeth are to exfoliation. If he’s nine and no perm teeth you probably aren’t getting away with waiting because they will have those primary teeth longer than normal. You may have 4 more years with those teeth in a kid with late eruption and you would be playing with fire. It would be a little weird to be nine with no perm teeth though not going to see that very often so you may want to check your records there