Trust your instincts. He may very well not be ready and may benefit from waiting a year. He'll be in school for at least 13 years -- any extra year spent at home now may provide the time for him to mature just enough to start kindergarten. Why rush to put him in kindergarten if you believe he's not ready? Boys especially may take a little more time before they can sit still in class, concentrate, listen, follow directions, etc. It's very hard on a little boy to "behave" in school if he's not ready. Remember, the beginning of the next school year is nine months away - that's a long time during which there's so much development and growth in a child that age.
Educators are just starting to recognize differences between teaching boys and girls -- especially during the first years of school. I have two grown sons and four young nephews and can tell you teachers tend to be tougher on little boys. Enjoy your little one at home for another year if necessary and don't worry about it.
Good luck and Merry Christmas!