The fortysomethings I know also think it's only for old folks. Do thirtysomething's still use Facebook ironically, or something?
Not among my peers. Facebook is seen as a way to communicate with older and tech-challenged relatives. It's in the same category as LinkedIn -- a social network whose content is mostly cringe and that you're only on as a means to an end, not because it's a good product.
I had an account years ago but abandoned it as soon as they started to monetise (same for Twitter).