I actually have some insights and experience on this issue in a range of different hobbies, and generally speaking the news isn't any too good for the most part. Those who know of situations that are seeing generational involvement, I most certainly congratulate them, but they are bucking the general trend. Steam may, or may not, be an exception to the general trend of "old time" hobbies, but many of the traditional pastimes that us older folks grew up with as kids, are rapidly becoming extinct. The reasons for this may be many and varied, but the trend is pretty irrefutable in the venues I'll refer to here.
Let us take stamp collecting, Philately if you will, as an example. I have a 1991 Scott catalog that I am still using to this day as it serves its purpose adequately for my needs. However, because it is so out of date I must of course adjust the values listed in it to bring it up to the current market. To make that correction I generally apply a factor of from 30 to 70% DOWN on the prices listed in that nearly thirty year old catalog, to bring its prices in line with today's market. The reason for this is that the great collections amassed back in the 50's - 90's, by the folks who became parents and then grandparents, are now coming onto the market through estate sales that sell a whole volume for less than the original value of just a few of the stamps held within, and the reason this happens is because none of the heirs care! Thus the market is now glutted with what were once desirable collectibles, that ever fewer people now want nor care about.
True, some of the most desirable and collectible rarities do still bring new record prices, but that isn't the real hobby of stamp collecting, it is the offshoot of rarity investing, and that will still go on, among a very small and mostly exclusive part of the population, and reflects not at all on the original hobby level pursuit.
As another example let me offer HO scale brass import locomotives, the most highly sought after and desirable models of the 1950's thru 1980's. They have actually held their original values pretty well, and for some special and less common models have actually posted fair gains. But, and this is a big but, the actual value of the dollar in the same time period has eaten those numbers back down to substantial actual losses in value. The reasons are much the same as with stamp collecting, with a few added twists. The folks of an age that collected these works of mechanical art are leaving them for the most part to uncaring heirs who have no intention of building a layout and making any use of them, nor of holding and displaying them as a collection. Brass engines are actually still being built and imported, but to a wholly different standard of operation and detail, but even these are being offered to a rapidly diminishing market, as the commitment and craftsmanship needed to build an operational layout are mostly outside of the interests of those who are young enough to take up the challenge. Thus another hobby that was robust and thriving in the not too distant past, is now passé.
I could list several reasons why I believe this to be happening to "physical" hobbies en mass, but I'll leave that to another time and post. For now I'll just say that I truly believe this to be a general trend in most of the traditional hobby activities, with some individual exceptions no doubt!
Sorry for the doom and gloom .... I'll just ignore the trends I see, and enjoy those activities that continue to make me happy!!!