This is a ridiculous comment. People under 30 are probably more engaged in hobbies than ever. For the record, I am 42 at the tail end of Gen X. Must of my friends though are solid Gen X'ers with none being under 50. However I can see what is around me and I work with a lot of millenials and people under 30.
Here are some facts:
1. Trains, especially O Gauge take up a lot of space (yes, you can have small layouts, however for most that doesn't hold interest for long)
2. Trains, especially O Gauge are expensive (yes, you can go less expensive but even setting up a decent postwar layout isn't cheap)
3. Trains are a niche for a hobby, you have to have an interest in trains in general
4. There is a larger variety hobbies today than ever before, especially around outdoor activities which I see a lot of younger people engaging in
5. Trains are mostly a solitary hobby (yes there are train clubs, however they are not convenient to or of interest to many for a variety of possible reasons, clubs have their own challenges)
During this lock down, if my 13 year old's hobby was trains, he would have been by himself isolated with just me. However, he loves Xbox and playing with his friends, which has kept him socializing and working with others the whole time. It takes a lot of active teamwork on these multiplayer games. Even though I myself as a gamer don't care for that style, I respect it.
For people who say the younger generation doesn't like building, using their hands, etcetera, you need to get out of your bubble. A quick look at YouTube disproves this easily. I see millennials building guitars from kits, restoring antique items, modding their cars, building their own Lego creations, making amazing static models in ways never seen before, converting old vans and trucks into RV's, re-purposing multitudes of things, building their own guns, building and modding RC vehicles, making furniture, designing, 3D printing and building custom projects, building and modifying mountain and street bikes, electric bikes, and so on, the list is never ending.