Your son might be a little shy

and not sure what to say. I find a lot of teeagers or even early 20s really have no interest in talking to people who are a lot older than them. It can come across as rude sometimes. I found my new neighbour's daughter is the same way. They came to my house and I invited them in. Mum is chatty but the daughter never looked at me or say a word. All the time they are in my house her eyes are on her cellphone. I took it as they have no interest in talking to other people that is not their age.