“My spirits.... now lean towards sadness and melancholy. I too am beginning to feel my age. Then, as one moves on in life sorrows multiply, and necessarily it is harder to keep cheerful... [I experienced] violent disappointments, that I might even call grief.”

Source: Atlas Shrugged

Quoted in A Thousand Days: John F. Kennedy in the White House, Arthur Schlesinger (Boston: Houghton Mifflin Company, 1965), page 1017. http://www.jfklibrary.org/Research/Research-Aids/Ready-Reference/JFK-Quotations.aspx According to a footnote in Schlesinger's manuscript (1st draft, page 1378), this was stated on February 13, 1961.
Attributed

http://sports.espn.go.com/espn/print?id=2083509&type=story
On boxing

Variant: I drank because I wanted to drown my sorrows. But now the damned things have learned to swim, and now decency and good behavior weary me.

2010s, 2018, Farewell statement (2018)
Context: I have tried to serve our country honorably. I have made mistakes, but I hope my love for America will be weighed favorably against them.
I have often observed that I am the luckiest person on Earth. I feel that way even now as I prepare for the end of my life. I have loved my life, all of it. I have had experiences, adventures and friendships enough for ten satisfying lives, and I am so thankful. Like most people, I have regrets. But I would not trade a day of my life, in good or bad times, for the best day of anyone else’s.
I owe that satisfaction to the love of my family. No man ever had a more loving wife or children he was prouder of than I am of mine. And I owe it to America. To be connected to America’s causes — liberty, equal justice, respect for the dignity of all people — brings happiness more sublime than life’s fleeting pleasures. Our identities and sense of worth are not circumscribed but enlarged by serving good causes bigger than ourselves.
"Fellow Americans" — that association has meant more to me than any other. I lived and died a proud American. We are citizens of the world’s greatest republic, a nation of ideals, not blood and soil. We are blessed and are a blessing to humanity when we uphold and advance those ideals at home and in the world. We have helped liberate more people from tyranny and poverty than ever before in history. We have acquired great wealth and power in the process.

III, ix, 35; translation by Arthur Leslie Wheeler
Epistulae ex Ponto (Letters From the Black Sea)

Letter to Gilbert Imlay (19 August 1794)