Hugo provided verifiable evidence from 1966.
This colloquialism for ‘extremely easy’ was added to the dictionary in 2002. OED editors posted an appeal for earlier evidence in our print newsletter back then, and we haven’t given up. We’re still trying to find evidence earlier than our current first quotation:
1976 Evening Standard 20 July 19 (caption) I’m short of money this week. How do I get to work? Easy peasy. I run to the station, leap the barrier, clobber the train driver, dress up in his clothes [etc.].
Earlier evidence may be available in print, or in new digital archives which were not available when we initially researched the entry.
Posted by OED_Editor on 28 November 2012 10.12