As a younger person who in theory is interested in model railways, the sad truth is that the drawbacks simply outweigh the benefits.

Model trains are physically large, so building a layout in my apartment is pretty much impossible. They are extremely expensive, and if you want to get something which can do more than literally run around in a circle you're looking at a $X000 setup cost. The "sexy" part (digitally controlling the trains) seems to be pretty much stuck with poorly-designed protocols from the 80s.

I like trains. I like DIY electronics. I like 3D printing. But given the barrier to entry, I'll just stick with OpenTTD or some kind of Euro Train Simulator game.

My friends are into Warhammer and DIY racing drones. If those hobbies have no trouble attracting younger people, the problem here really isn't young people's interest.