Without delving into all the minutiae of all the points brought up:
We need to be careful when saying kids just aren't into hobbies anymore, basing it on just the overall train hobby.
Around my area which is west of the Mississippi, the following shops that cater to these are always full, especially on weekends, with kids and their parents:
R/C Hobbies, especially on-road and off-road racing. We're talking vehicles you build, and then modify to your liking. Not the $65 off the shelf Toy R Us C-Cell powered things. For a decent basic setup, the entry cost pushes upwards of $500. Many of the shop also have a track, either outdoor or indoors. It's a lot of fun. The kids in this hobby learn a lot of things as they build, race, analyze, and so forth.
Robotics is a huge up n comer:Kinex, RokNBok, and so forth. A couple hobby shops near me have converted entire sections to this area.
Science Clubs devoted to 'Robot Wars' is very popular.
As a natural part of this generation of kids, coding and software design is big. I am beginning to see clubs setup around this.
All of the above involve healthy socialization.
The kids are alright
Last: The number one demographic of kid 13-19 playing video game whether on an OS device or a PlayStation, are athletes. Not exactly a sedentary bunch.
FYI: I just turned 60, and in addition to trains, I also play video games
