Hi C. A---It's a tough question. AS others have done, I'll tell you our story. Our oldest, a girl, has a late Nov. birthday. She had been accepted into a head start program for at-risk pretty much based on her shyness. She did great in school, however and we were told she would be fine. This really gets me, but the teachers told us that if there were any academic challenges, they usually catch up by 3rd grade or so. Frankly, based on her personality, we weren't worried about academics, we were concerned about emotional issues in middle school...girls that age can be downright evil. We held her back and academically all was good. The social part still was a challenge so I'm so thankful she was a year older going through that.
BTW...Amanda is 27 now. When she started school the state of Michigan was talking about changing the start date to September back then. I wouldn't hold my breath.
Our other 2 are boys. Thomas has a July 17 birthday, about the same time as your little guy. He did just fine, but he's a second child.
We moved to Illinois when our youngest was 4. He has a late Sept b'day. He could not start school, even tho his b'day was 3 wks after it started. He was actually reading at that time. (Much credit goes to his brother as they shared a bedroom...T is 4 yrs older than Ian.) So yes, he sometimes had problems working without disturbing others...he was a bit bored but we never felt that to be an issue, more so for the teacher. You just have to be his advocate with his teachers and have them give him extra work to challenge him.
Bottom line, as I see it, he will have to grow up fast enough without starting school young. Let him be little for one more year. As others have said, you know him best, but I think that you'll always have the opportunity to have him advance a grade, which would be so much better than having to hold him back. He will most likely, if academically gifted, be put in advanced classes as he gets older, and will be in a great position as he looks toward college. Feel free to contact me if you'd like to talk more. Good luck...D.