You and her are separated?

If you want your kids to be smart, read to them. Start early and read a lot. Instead of watching TV sit on the couch and read books to them. I'm not talking children's books, but good books. My wife read to the kids about an hour a day every evening almost. She read books like the Hobbit, Little House on the Prairie, Sugar Creek Gang, Entire sets of books, dozens of books. Three of my five kids were valedictorians, the others could have been if they wanted to be. Maybe some of it's in the DNA (I'd like to think that anyway) but mostly the kids are so bright because they learned so much so early and took it from there.

"I want him to be with kids his age."
Certainly, find an academic setting that will challenge him, but don't put him in a situation where he has to spend all of his time with older kids. This, I believe is very important. I have an IQ of 160+, and my parents, because of heavy pressure from my teacher and the school principal, had me skip 4th grade. I was already young for my grade (June birthday) and this made me the very youngest in my grade. I ended up in elementary and junior high classes with kids who were sometimes more than two years older than me.
The results? I was always very awkward socially. What girl wants to go to Junior Prom with a guy who isn't old enough to get a driver's license?
Even though I was also physically advanced, I had difficulty competing in team sports. As a 14-year-old sophomore in high school, I was playing against guys who were sometimes five years older than me. Because of insurance laws, getting a job was nearly impossible until after I had graduated.
Some of this may sound trivial to adult readers of this forum, but believe me, these and other issues seemed like life and death to a young boy unsure of where he fit in.
For your son, please try to balance his social needs with his intellectual needs.

Another thing to consider is this: A formal school isn't always the best choice. If you look at the life of people like Albert Einstein, R. Buckminster Fuller, George Bernard Shaw, Albert Schweitzer, etc. they all had substantial periods of unstructured learning in their early years. They weren't "in school," but if they were awake, they were were learning. They were following their own paths, and learning either what stirred their curiosity or what they perceived as necessary. You can foster this self-education by providing your son with tools like a globe and an atlas, a microscope, Lego and construction sets, an abacus, all the books he could desire, pet animals, gardening tools - as much as you can afford.

Your boy is fortunate to have parents as aware and committed as you and your wife.