
Lincoln-Douglas Debates http://www.nps.gov/liho/learn/historyculture/debate1.htm (21 August 1858)
1850s
AP report with lead summarizing of remarks stating "Robert F. Kennedy said yesterday that the United States — despite Alabama violence — is moving so fast in race relations a Negro could be President in 40 years." "Negro President in 40 Years?" in Montreal Gazette (27 May 1961) http://news.google.com/newspapers?nid=1946&dat=19610527&id=y40tAAAAIBAJ&sjid=F50FAAAAIBAJ&pg=5424,5208719
Context: The Irish were not wanted there [when his grandfather came to Boston]. Now an Irish Catholic is president of the United States … There is no question about it. In the next 40 years a Negro can achieve the same position that my brother has. … We have tried to make progress and we are making progress … we are not going to accept the status quo. … The United States Government has taken steps to make sure that the constitution of the United States applies to all individuals.
Lincoln-Douglas Debates http://www.nps.gov/liho/learn/historyculture/debate1.htm (21 August 1858)
1850s
The Ballot or the Bullet (1964), Speech in Cleveland, Ohio (April 3, 1964)
From interview with Subhash K. Jha
“As for whether Perl 6 will replace Perl 5, yeah, probably, in about 40 years or so.”
"Developers can unwrap Perl 6 on Christmas", Infoworld, 2015-12-21 http://www.infoworld.com/article/3017418/application-development/developers-can-unwrap-perl-6-on-christmas.html
Other
The Second Declaration of Havana (1962)
As quoted in "Socialism is So Hot Right Now" https://www.commentarymagazine.com/articles/socialism-hot-right-now/ (17 September 2018), by Jonah Goldberg, Commentary
1990s