[HGSW0904]

It was first said by Francois Guisot, a French monarchist statesman:

“Not to be a republican at twenty is proof of want of heart; to be one at thirty is proof of want of head.”
(Said in reference to whether France should be a republic or a monarchy.)

It was later adapted by French Premier Georges Clemenceau:

“Not to be a socialist at twenty is proof of want of heart; to be one at thirty is proof of want of head.”

[scripter]

It appears Guisot is the orginator. I was thinking of George Bernard Shaw but that isn’t correct either.

[Michael.SF.]

It was first said by Francois Guisot, a French monarchist statesman:

Excellent, thank you.

I believe you are right, he was the originator and various people over the years have used it, or a variation of it. Churchill's being the one seen most often. Now I will search under Guisot's name and find other variations.

[Michael.SF.]

Guisot (also spelled as: Guizot) appears to be correct. Here is a link to an excellent explanation, which has other links to confirm this:

“Not to be a republican at twenty is proof of want of heart; to be one at thirty is proof of want of head.”

In the above link it is also stated that variations on this quotation were later attributed to Disraeli, Shaw, Churchill, and Bertrand Russell.