heartcreature

If this teen is autistic he's not interrupting the conversation on purpose. He just doesn't understand the social cues. You could describe him as being very self centered. When there is a conversation he may be assuming that he is part of that conversation and that you should be wanting to talk about what he wants to talk about. What seems nonsensecal to you is not to him. It makes total sense and you may be the nonsensecal one in his eyes. He may be thinking this: How could she possibly want to talk about anything other than what I think is fun to talk about? Think about it this way. Suppose you are very near sighted but there was not a way to test your vision and no way to correct it. Others who didn't have the near sightedness would see things differently than you but they could never explain it in a way that would allow you to see it the way they do. That's the way social situations are to an autistic person.
Could the mother be more helpful to her son it's possible, but I can tell you that being the mother of an autistic 19 year old it's very overwhelming at times and you just plain get tired. The norm for a family dealing with autism is much different than other families. It's often easier for the entire family to change than it is to try to change the autistic person.