People (particularly women) often pick up the game later in life. Nobody starts playing in a basketball league at age 55. But the age of golfers doesn't worry me. When I was a kid 30 years ago, I remember sports writers talking about baseball's imminent death, because of the ages of fans. Here we are, a generation later, and MLB is the second richest sports league in the world, not all that far behind the NFL in revenues.
The problem private clubs are facing has less to do with golf and more to do with changing socializing patterns. Couples used to go out for drinks at their club, dinner at their club, parties at the club. Now, people tend to be more mobile, and socialize with broad groups. Because of that, membership is less appealing.
Country club food (while improving significantly the past fifteen years) is still old school fine dining. Foodies like myself don't want to eat that shit. Herb roasted chicken breast and filet mignon. zzzzzzzzzzzzzzzzzzzzzzzzz....
I've seen contraction in the Pittsburgh area. Some clubs have gone semi-private, one closed entirely, etc. Lowering fees to join and eliminating bond purchases. This is just a natural reaction to market forces. A regression to the mean. Golf isn't going anywhere and all this hand-wringing over it's future is pointless.
And you're right about the equipment manufacturers fueling much of this. As if it's the sport's job to keep their companies profitable. Hey, cut costs and put out a better product like every other industry you goddamn clowns.