Our daughter is a November baby and her kindergarten school allowed early entry - she was SOOO ready for it, academically as well as emotionally. I think you have to have both to be confident putting your kid in early will be successful.
My son on the other hand is a December baby and the school district we were in at the time did not allow early entry at all, so we enrolled him in a head start program instead, 3 hours a day, weekly... so he finally enrolled in K when he was 5 and 7 months. And it was a miserable experience. He hated school. Every day he would cry that he didn't want to go. He wasn't being bullied, he just couldn't sit still for as long as they required and he was so bored! To make matters worse, his teacher didn't believe in testing Kindergartners for gifted, so we never even got the chance that year to get him tested. In first grade he was tested, and we even had to move him into the "gifted" teachers class, but it was a much better year for him, being challenged with work though we still have issues with him not wanting to sit still for any length of time.
All that to say, if we had been given the opportunity to put him in early, we would have taken it - thinking he was academically ready, and likely regretted the decision. He was no-where near ready for what traditional school requires at that age.
