The reason I'd be comfortable calling it immature is that shallow relationships with people are common in the young, but most people grow out of it. And very few go back from treating other humans as equal to a more narcissistic approach.

I don't think there's anything essentially wrong with narcissism. Toddlers believe the whole world is about them, and have to be trained not to hit others. Gradually, we learn that other people are independent entities, just as real as we are, and just as deserving of respect. I think that's a life-long process. This guy seems way behind for his age, which is also my age. I hope his time off lets him catch up.