Don’t know for sure but it goes back decades if not centuries. Europeans often do it slightly differently to reduce confusion - they use roman numerals for the month so for August 7 1961 you might see 7/viii/1961 but they still put the month in the middle, not first.
From this website in a thread called "American vs British style of writing dates":
http://www.antimoon.com/forum/t1952-45.htm
David Thu Jan 11, 2007 9:32 pm GMT
What a stupid discussion:
Fact is:
Both day-month-year and month-day-year are used in Britain. And the month-day-year version is even preferred by British newspapers:
Let's see:
The Times: February 17, 2005
Guardian: Feburary 17, 2005
Economist: February 17th 2005
And there are also influential American publications (especially academic publications) that use day-month-year, for example:
Science Magazine: 17 February 2005
Physical Review Letters: 17 February 2005
****
and from Saturday's Times of London, check out the date, September 5, 2009:
.
Roman numerals??