A visit to a major university is in order. Specifically visit the department heads of the department of mathematics and the department of physics, by appointment. They will know, or will be motivated to find out, the very best educational programs for your grandson.
Just as importantly, there are people you should make every effort to steer clear of, as they will see your grandson as little more than an experiment whose time they can freely waste. These include child psychologists, child developmental experts, and others who want to use them for their own purposes, not provide opportunity to them.
Children who are intellectually gifted will face a great deal of resentment, ironically far more from adults than from their peers, and the gifted educators found in mathematics and physics still vividly remember the unnecessary obstacles that were laid in their own paths, so may offer particularly good advice.
Best of luck.
Thanks you all so very much for your empathetical and insightful responses to my post about my grandson. Many of you mentioned sports and music. He plays in a soccer league, loves to long-distance run and hike with his Dad, takes swimming and gymnastic lessons, and has recently developed an interest in golf. He has always loved music and his maternal grandfather is teaching him to play the guitar and banjo. He picks out tunes on the piano, as well. I sometimes worry about him taking on too much too soon. But we just follow his lead.
At the risk of sounding a bit too proud, I would like to say that he was fortunate to be born into the life he has. Most of the adults on both sides of the family are college educated, many with advanced degrees, many of us are/were educators. Many have mathematical and scientific educations.
But, my greatest source of pride is that we are a large, loving, supportive and protective family. He has some great role models to admire and dozens of cousins to keep him grounded in reality.
We will all work together to shepherd him and keep his path true.
What a collection of great minds you all have. FReepers are the best! Thanks again.