Has your son had many opportunities to play with children his age? Has he been involved in group activities? He'll need a great number of these experiences in order to handle kindergarten. In fact, good social skills are absolutely vital to success in school at all grade levels.
Keeping your son home next year will not help him develop the skills needed to get along with other children. He needs to learn these skills through playing frequently with children his age. Embark immediately on a plan that will help him feel at home with his peers.
If your son is already comfortable playing with one or two children his age, it's time to introduce him gradually to group activities. Otherwise, concentrate first on giving him the opportunity to play with just one child in your home. The best playmate would be someone who would be in his kindergarten class.
Introduce your son to group activities in which you and/or a friend can also participate to give him confidence -- library story hours are a good choice. Then build upon this by having him take part in such activities as karate or swimming lessons so he will also learn to take directions from adults. Once he becomes more comfortable with children his age, consider enrolling him in a preschool, Sunday school, sports, or park program this summer.