While it would be nice to have younger people in the hobby, it is not essential. My best examples are model railroading and wooden sailing ship modeling. These both have always been primarily adult hobbies. Sure, there were a few teenagers in each (I was one of the few) they have been primarily adult. Yet, the hobbies are as strong today as ever.
When I was a kid, certainly there were many other kids building models. But what we built were Revell and Monogram kits that were pretty basic. They were ALL styrene. There was virtually NO aftermarket business. Then, for decades there were aftermarket decal sources.
Now, for so many kits we can buy extra photoetch accessories, resin detail parts, conversions, etc. Scale modelers have never had it so good.
I suspect mail order and internet sales are taking a toll of ALL forms of retailers, not just hobby shops.
So enjoy the golden era of scale modeling (the present). Don't long for the good old days when if you wanted an obscure model you scratched it, and if you didn't want to scratch-build or heavily modify kits, you had little to pick from. You painted models with hardware store enamel 'cause model airplane DOPE attacked plastic and no one was selling plastic model paints. All paints were glossy. If you wanted a flat finish you added talcum powder to the paint.