I have a spring birthday boy who skipped first grade. I think that there is something to be said about starting in K - it is mainly about learning the social/group aspect of school and the activities will not be challenging perhaps but still fun.
It also gives you time to see where he is at academically towards the end of the year and then start brainstorming/planning.
That being said...most kindergartners in full day programs come home whipped until later in the year as they get used to it. And most full day programs have a rest and less academic activities in the afternoon so maybe he would be okay all day.
