This one is pretty much, in my humble opinion, a "toss-up" between the two.
The quote has been attributed to Mickey Mantle, Eubie Blake, George Burns and Mark Twain (amongst others).
Here's one of them with a citation-
"If I'd known I was gonna live this long, I'd have taken better care of myself. "
~James Hubert (Eubie) Blake (1893-1983), On reaching the age of 100, quoted in Observer
(13 Feb, 1983): 'Sayings of The Week'
Here are some others:
This is the definitive source for healthcare information available online. More than a directory of Web sites, this book combines a plethora of URLs with useful information on the key health issues facing us today. I especially appreciated the Mickey Mantle quote in Chapter 16: 'If I knew I'd live this long, I would have taken better care of myself.'
Hopefully, with the information referenced in this book, I can take better care of myself, and in turn, live longer.
~reader review of "Healthcare On-Line for Dummies"
http://shop.barnesandnoble.com/booksear ... 0764506846
The "Baseball Almanac" gives it to Mantle
"If I knew I'd live this long, I would have taken better care of myself."
- Mickey Mantle
And it is revealed here, that Mantle "appropriated" the line from:
Mantle was friends with Bobby Layne, the star quarterback for the Detroit Lions. It was from Layne that Mantle appropriated the line: "If I had known I was going to live this long, I'd have taken better care of myself."
~from Mantle was charisma defined, By Larry Schwartz
Special to ESPN.com
“We used to tease each other about whose liver was going to go first. I never thought it would end for him this way,” said Mantle. Part of the reason for Mantle’s high living was his suspicion that he would follow his father and grandfather to an early grave. At age 46 he said, “If I knew I was going to live this long I would have taken better care of myself.”
~author unknown, found at