I've heard a lot of pros and cons about starting kindergarten early. Some people say you should wait so that the child is more socially-emotionally mature. I also saw an article about a study saying that starting kindergarten early is correlated with increased ADHD (but I don't have access to the original study, so I don't know whether it's a causal relationship or just a correlation -- e.g., gifted kids are more likely to both have ADHD and start kindergarten early -- does anyone have more info on this study?)
I've seen some of those studies. They tend to be just focused on the general population instead of the gifted population, which does mean that you might not want to use the general case if you believe you are the exception. In addition, I'd recommend reading
this article. It deals with the long term consequences of redshirting (delaying entry) on kids and not just the short term. That is, yes, there is some evidence that delaying entry to school decreases adhd and behavior problem diagnoses, it also never teaches kids how to control impulsive behavior or control emotions. Long term, being the youngest helps much more than it hurts.
That said, do you think he's ready? Another option could be preschool and then entry into 1st grade (skipping K).
