I started with a small setup in my basement circa 1985, The kids were 1 and 3 years old. My father-in-law was an antique dealer and came across many trains. For birthdays and holidays he would always have a few of them for me. As years went by neither of the kids stayed interested so when they were about 12 I packed it all up. Fast forward 15+ years, the kids are gone and now they want a train set for their houses.
Almost two years ago I re-opened the train boxes and started getting sets ready for each of them. I even put a set around my tree. My wife watched as I sat at the table while she read and I cleaned and oiled and tested train after train. She realized how much I was enjoying myself and she suggested after Christmas I put up a layout in the basement (new house).
I had no idea how far the industry had come in those twenty odd years. In the last two years I switched to totally Legacy and DCS and have spent hundreds and hundreds of hours on my layout. The kids love coming over now and seeing what I have added (they are 25 and 27). They help me with the electonics and the scenery construction. They can't wait for the Holidays to put a bigger and better track under their own trees.
My point is as long as people are exposed to things when young it remains in their head and bcomes a cherished memory. When they get older and have time, room and a few bucks they will want to relive those memories. Show as many young people as you can you layouts. Plant the seed.
My grandkids can run the DCS and Legacy better than me!!! (kidding)
Jeff