My mother is a private school second grade teacher and she ALWAYS suggests that if a child has a late birthday for their class (summer or early fall), they should wait to enter Kinder until they will be one of the oldest in the class, ESPECIALLY with boys. She says it often has nothing to do with "smartness", but more social and other developmental aspects. She has seen it time and time again that a "late" birthday child needs to be in the class below them but were rushed into school. She said they even usually get along better with the class below them on the playground.
Of course, you can hold them back in the younger years without any havoc on them, but why rush?!?! Just let him develop on his own. One more year in pre or with you is better for him anyway! Let him start ahead instead of behind!
My son is a may birthday, and although he is only 9 mos old, we have already considered that he may not be ready for kinder when he is ALLOWED to enter! We will wait and see, but too, I don't know if I want him to go through his entire senior year in high school only being 17. If I were in your shoes, I wouldn't want my son graduating H.S. at age 17 either. Though it is not bad by any means, wouldn't it be nice if he was 18 when he entered college? Just a thought!
Best of luck on your decission but remember that there is no need to rush a child! Let them be children and learn at their own pace! Why rush when it will not harm them and may even help them be more secure in life!
T.