I'm 52 and my son is 12. His interest in "our" trains comes and goes. He had one of his friends over the other night for a spend the night. The boy had never seen the trains and was really impressed for about 15 minutes then they both returned to the Xbox and PS4.
One thing that has really helped him is his being able to run the trains AND doing so from the iPad (thanks MTH). Also I have found getting engines and cars that he is interested helps a lot too. He is interested in army items so a train with tanks and half tracks on flat cars was a big hit.
I was talking about the trains to him yesterday and said when I was his age I remember going to Toys r Us and there being an entire aisle of just trains. He was blown away by that, he asked me if i was joking. I also told him that growing up nearly all my friends had a train layout of some sort at their house, again a similar response.
The world is vastly vastly different today than it was 40 years ago and am sure will be more so in another 40 years.
John