I have heard it as, "anyone who was not a liberal at 20 years of age had no heart, while anyone who was not a conservative at 40 had no head." In his time/era, what are the definitions of conservative/liberal and how do they differ from modern day definitions?
This is a misattributed quote that Churchill never said. From the International Churchill Society's site:
There is no record of anyone hearing Churchill say this. Paul Addison of Edinburgh University made this comment: 'Surely Churchill can't have used the words attributed to him. He'd been a Conservative at 15 and a Liberal at 35! And would he have talked so disrespectfully of Clemmie, who is generally thought to have been a lifelong Liberal?'
He says "Celui qui n’est pas républicain à vingt ans fait douter de la générosité de son âme; mais celui qui, après trente ans, persévère, fait douter de la rectitude de son esprit." This translates to "He who is not a republican at twenty compels one to doubt the generosity of his heart; but he who, after thirty, persists, compels one to doubt the soundness of his mind".
Churchill never said this quote and it's been attributed to many others. It seems that it's just a rewording of Jules Claretie's old quote that has come into the popular consciousness.