When I started in HO the average age of a model railroader was early adulthood to the mid 30s and since there were plenty of senior citizens in the hobby back then that meant there was a really large supply of young modelers, meaning beginners, to put the average where it was. It would be interesting to know what the mean age was back then but nobody was doing statistical gathering like that. My hunch is that there were actually relatively few model railroaders of the so-called average age of 25 to 35.
Result: lots of model railroad goods aimed at beginners, which in turn had an impact on pricing and availability, and frankly, on prototype accuracy as well. Everybody complained that it seemed like the only road names available were the Santa Fe, Union Pacific, and Pennsylvania Railroad. The guys who modeled those three railroads seemed like kings of the hill. Fewer noticed or mentioned that those models were rarely accurate for Santa Fe, UP, or Pennsy.
Now the average age is post-retirement and getting older, not because more seniors are in the hobby but because there are fewer on the other end of the age spectrum to drag down the average. We often already have all the track and control systems we'll ever want, we're up to our armpits in locomotives and rolling stock, and now our interests are more granular like scenery, more specialized in era and locale, better informed about prototype, and quite possibly not shared enough with other local modelers to support a money making train store.
Dave Nelson