That quote has been changed a bit, but in it’s original form I think it was Churchill.

And the general idea is that as you age your idealism is tempered by practicality, as well as having adapted to the situation and built something of a life of your own, so you’ve gradually moved from the camp of “very little to lose/give up in exchange for all these benefits” and toward the camp of, “you know what, I’m doing okay, I’ve figured out a way to make it work, and I’d rather ‘the system’ just leave me alone at this point, since I’ll be footing the bill for things that aren’t even going to benefit me that much”.

Obviously it’s a lot more complicated than that, but that’s the gist.

It’s also worth remembering that “liberal” and “conservative” meant something different mid century than they do now. Especially with the MAGA influence.