But with “A Knight of the Seven Kingdoms,” unlike some other HBO productions where the adult content just is the content, it’s relatively easy to imagine a version that’s fit for youthful eyes. Or at least a version that has just that one scene where you’d fast-forward while otherwise keeping things PG-13. So I’ll use the show’s failure to be a youth-friendly production as an excuse to express frustration at the dearth of popular art that falls in that zone — telling grown-up stories in a fashion suited to the ages between, say, 10 and 16.