“My heart leaps up when I behold
A rainbow in the sky:
So was it when my life began;
So is it now I am a man;
So be it when I shall grow old,
Or let me die!
The Child is father of the Man;
And I could wish my days to be
Bound each to each by natural piety.”

My Heart Leaps Up When I Behold, (1802)
The last three lines of this form the introductory lines of the long Ode: Intimations of Immortality from Recollections of Early Childhood begun the next day.
Context: My heart leaps up when I behold
A rainbow in the sky:
So was it when my life began;
So is it now I am a man;
So be it when I shall grow old,
Or let me die!
The Child is father of the Man;
And I could wish my days to be
Bound each to each by natural piety.

Many Long Years Ago (1945), Song To Be Sung by the Father of Infant Female Children
Context: My heart leaps up when I behold
A rainbow in the sky;
Contrariwise, my blood runs cold
When little boys go by.
For little boys as little boys,
No special hate I carry,
But now and then they grow to men,
And when they do, they marry.
No matter how they tarry,
Eventually they marry.
And, swine among the pearls,
They marry little girls.

Not found in Twain's works, this was attributed to him in Reader's Digest (September 1939): no prior attribution known. Mark Twain’s father died when Twain was eleven years old.
Disputed
Variant: When I was a boy of fourteen, my father was so ignorant I could hardly stand to have the old man around. But when I got to be twenty-one, I was astonished at how much the old man had learned in seven years.

If 6 Was 9
Song lyrics, Axis: Bold as Love (1967)
Source: Jimi Hendrix - Axis: Bold as Love

"One of his most famous and most quoted remarks. First printed in the Boston Globe, June 16, 1930, after he had attended Tremont Temple Baptist Church, where Dr. James W. Brougher was minister. He asked Will to say a few words after the sermon. The papers were quick to pick up the remark, and it stayed with him the rest of his life. He also said it on various other occasions" ~ Paula McSpadden Love <!-- (p. 167) -->
Variant: I joked about every prominent man in my lifetime, but I never met one I didn't like.
John D. [Rockefeller] sure carried out my old saying, “I never met a man I didn’t like.” Nationally syndicated column number 219, Rogers Gets Six Shiny Dimes From Oil King (1927).
The earliest dated citation of such a remark thus far found in research for Wikiquote is the one from 1926 about Leon Trotsky from the Saturday Evening Post (6 November 1926).
The Will Rogers Book (1972)

Quoted in A Few inches of Ivory, 24 November 2013, Jstor Organization http://www.jstor.org/discover/10.2307/23001425?uid=3738256&uid=2129&uid=2&uid=70&uid=4&sid=21102981873241,

Source: Beastly

That's a sign of respect that my father didn't get, that my brother didn't get, that my mother didn't get.
Attributed

Confessions of a Philosopher (1997)
Context: Speaking for myself, I am not one of those people who are able to deal with the problem by ignoring the questions: it may be a matter of temperament, but for me the apparent unanswerability of the questions sharpens the persistence with which they nag at my mind. Scarcely a day has gone by since my childhood in which I have not thought of them. In fact, the truth is that I have lived my life in thrall to them. They seem to me obviously the most important and interesting questions there are, and in my heart of hearts I do not really understand why not everybody sees them as such. And yet at the end of it all I have no solutions. I am as baffled now by the larger metaphysical questions of my existence as I was when I was a child — indeed more so, because my understanding of the depths and difficulties of the questions themselves is now so much greater.