It might help to elaborate on what type of kindergarten it is - full day, half day, play based, academic focused, Montessori/Reggio/other, etc. When is his birthday relative to the cut off? (ie. if he started without acceleration his birthday is 4 months from the oldest or something along those lines) Do lots of people red-shirt in the area?

(sorry I'm answering your question will a million more but I think they will help in the end)