I think, you have a very sensitive child. There is something going on which your DS is picking- will be worth to talk to the teacher or try to understand it from your son.
I don't think that your son is not mature, he just has a bigger brain and can sense, analyze and feel the things, most kids of his age can't. The behavior stemming from it at young age, is portraying him as being immature at times- to be precise socially immature.