@sherri2000,
If he's smart, he'll be bored out of his skin sitting through kindergarten twice. If you think that he's not mature enough or still too impatient to handle the school routine, why not give him another year at home instead of an extra year of school?
He'll be in school soon enough, but won't have another opportunity to have a year with you and you with him once school starts.
My son was a young five when he started school - his birthday is in August. I went ahead and sent him because he was smart and big for his age and socially and behaviorally mature and adept and he did fine.
But looking back, I have to say that if I had it to do again, I'd have kept him home another year - just because they grow up so fast and that time is so precious- and you can never get it back once it's gone.