Almost certainly attributable to Oliver Wendell Holmes, Sr., who is, in various sources, credited with having said this in letters to Harriet Beecher Stowe (who turned 70 in 1881) and Julia Ward Howe (who turned 70 in 1889), as well as having made the commented about himself. Holmes, Sr. reached the age of 70 in 1879, while Holmes, Jr. reached that age in 1911, some time after the earliest reports of this quote.
Misattributed
“To be seventy years young is sometimes far more cheerful and hopeful than to be forty years old.”
Oliver Wendell Holmes (1809–1894) Poet, essayist, physician
On the Seventieth Birthday of Julia Ward Howe (May 27, 1899); reported in Bartlett's Familiar Quotations, 10th ed. (1919).
Michael Faraday (1791–1867) English scientist
Letter of Faraday to Christian Friedrich Schönbein (19 September 1861); see also The Letters of Faraday and Schoenbein 1836-1862 (1899), edited by Georg W. A. Kahlbaum and Francis V. Darbishire, p. 349 http://www.archive.org/details/lettersoffaraday00fararich
Kenny Dalglish (1951) Scottish association football player and manager
Bob Paisley ( Source http://football-rumours.com/kennydalglish.html) <br class="br">About
Sergei Akhromeyev (1923–1991) Soviet marshal
Quoted in "Mr. Darman's Sermon", July 29, 1989, editorial, New York Times.
Bill Nye (1955) American science educator, comedian, television host, actor, writer, scientist and former mechanical engineer
[NewsBank, Bill Nye defends evolution in Kentucky debate, The Times and Democrat, Orangeburg, South Carolina, February 4, 2014]
“They call me old, but I'm only 65-years old young man.”
Paavo Väyrynen (1946) Finnish politician
Presidential Election Campaign 2012
“Youth is not a question of years: one is young or old from birth.”
Natalie Clifford Barney (1876–1972) writer and salonist
In "Samples from Almost Illegible Notebooks", ADAM International Review, No. 299 (1962)
“The monetary system we have inherited is more than 2,000 years old.”
Margrit Kennedy (1939–2013) German architect
Source: Interest and Inflation Free Money (1995), Chapter Four, Some lessons From History, p. 89
