The people who told me that were 100% boomers. There’s that idiotic saying “if you’re not liberal* when you’re 20, you have no heart. If you’re not conservative when you’re 40 you have no brains” ok boomer.
Note this is using the US meaning of liberal, not to mean “capitalist”.
To the point at least. The impression I always got was that it was meant to imply you’d have money by then and not want to pay taxes.