— Abraham Lincoln 16th President of the United States 1809 - 1865
Misattributed, This quote is often misattributed to Lincoln. The earliest instance that Quote Investigator could locate was "in an advertisement in 1947 for a book about aging by Edward J. Stieglitz, M.D". The advertisement for “The Second Forty Years” which ran in the Chicago Tribune newspaper read like this: The important thing to you is not how many years in your life, but how much life in your years! (Compare 1947 March 16, Chicago Tribune, “How Long Do You Plan to Live?”, [Advertisement for the book "The Second Forty Years" by Edward J. Stieglitz, M.D.], p. C7, Chicago, Illinois. (ProQuest)). Source of misattribution: It’s Not the Years in Your Life That Count. It’s the Life in Your Years - Abraham Lincoln? Adlai Stevenson? Edward J. Stieglitz? Anonymous? by Quote Investigator on July 14, 2012 http://quoteinvestigator.com/2012/07/14/life-years-count/
To my way of thinking it is not the years in your life but the life in your years that count in the long run.
Adlai Stevenson II, Address at Princeton University, "The Educated Citizen" (22 March 1954) http://infoshare1.princeton.edu/libraries/firestone/rbsc/mudd/online_ex/stevenson/adlai1954.html. This has also been paraphrased "What matters most is not the years in your life, but the life in your years" and misattributed to Abraham Lincoln and Mae West.
Variant: It is not the years in your life but the life in your years that counts.
Adlai Stevenson II, "If I Were Twenty-One" in Coronet (December 1955).