It could be a case of avalible time and income, alot of mine actually went down the Airsoft route as its what was flooding the market when we were teenagers.
Many who were young in the heyday periods are now those towards the older end of things, their kids are grown and they are winding down so they are more able to revisit what they enjoy and have also the financial means to invest i their kit.
Doesn't mean the hobby will die with them though, there are definately younger people getting into them, you may however see forum usage drop as much of the sub 30 demographic do not bother with chat rooms or forums, some even barely use sites like facebook preferring newer things like Instagram.