ds knows pretty much everything, we are a very open house and I have 3 dcs and they all talk/ask questions and the others all earwig on the answers.
BUT he is year 6 and sex is disgusting, kissing is gross, puberty is embarrassing, anything relating to girls (like periods) is AAAARRGHHH.
So I think that the ''hands over my ears I can't hear you'' attitude isn't that unusual. I know ds talks to me because we have always had those conversations. He recently asked me something, about what contraception actually was, very red faced and embarrassed, but he said, well, it isn't rude, it is just a question, as he went bright red. I don't think he would talk about it if he wasn't used to it.
There is loads of playground rubbish that they hear. It is important he has real facts to hand, even if reluctantly.
I bought 2 books, Dr Christian's growing up book, very factual boys and girls, and the Usborne What's happening to me? For boys (but includes a bit about girls) which includes lots of feelings too.