There's an oft-repeated quote from Winston Churchill which goes something like this: "If a man is not a liberal when he is 18, he has no heart. If a man is not a conservative when he is 30, he has no brain."
Well, maybe you've heard it like, "If a man is not a socialist by the time he is 20, he has no heart. If a man is not a conservative by the time he is 40, he has no brain." Or maybe with different numbers, or different wording. The point is--well, the point is that Churchill never said that.
I went out looking for the exact quote on a whim (after looking for one of Churchill's other apparent quotations, which is, if true, wincingly racist and not likely to be pulled out in the ha-ha chuckle-chuckle aren't liberals stupid manner this one is). What I found was a page called Unquote, from someone else who went on this quest and discovered the same thing I did. You see variants of this quote all over, all of which sound perfectly plausible unless you actually do the research. (The page quotes George Bernard Shaw as saying "One who is not a socialist at 20 has no heart, and one who remains a socialist at 40 has no head," but Shaw remained a socialist until his death.)
That page quotes a book with the entertaining title Nice Guys Finish Seventh: False Phrases, Spurious Sayings and Familiar Misquotations by Ralph Keyes as describing the phrase as an "orphan quote," which may (or may not) have originated with Bennett Cerf reporting Georges Clemenceau's response to someone expressing alarm about Clemenceau's son being a communist: "If he had not become a Communist at 22, I would have disowned him. If he is still a Communist at 30, I will do it then."
However, I will share an actual quote from Churchill on the subject of liberalism, since I've gathered there's some confusion on the part of more flame-prone friends and acquaintances:
Liberalism is not Socialism, and never will be. There is a great gulf fixed. It is not a gulf of method, it is a gulf of principle. [...] Socialism seeks to pull down wealth. Liberalism seeks to raise up poverty. Socialism would destroy private interests; Liberalism would preserve private interests in the only way in which they can be safely and justly preserved, namely by reconciling them with public right. Socialism would kill enterprise; Liberalism would rescue enterprise from the trammels of privilege and preference [...] Socialism exalts the rule; Liberalism exalts the man. Socialism attacks capital; Liberalism attacks monopoly.
While this was in the time Churchill was part of the Liberal party in Britain (the subject of the article the quote appears in), it can be argued (and is, in said article) that Churchill remained true to his principles and shifted parties when he thought the parties' own directions were shifting. (Or more cynically, the political winds--the Liberal Party when he was a leader negotiated the "Irish Settlement" which led to all those years of peace between Northern and Southern Ireland for most of the last century, and that pretty much did in their political fortunes for a while.) After 1951 when Churchill became Prime Minister yet again, a close friend wrote, "At the root of his many-sided nature remains the essence of Liberalism."