um not normal for my kids! have fun for the next year exploring. I think some of the other parents might be more qualifies to offer opinion on this but I would suggest just making sure you are following DS lead and interests and encourage lots of play too so that he gets a good balanced. Sounds very advanced to me, but that also depends on how much you instructed him, and how much he asked for or just picked up. From my experience it's the traits rather than the knowledge that indicate giftedness such as early milestones (not that my kids were early), observant and perfectionism. Good luck
