Today, December 13, 2014, is the last day this century that the date as rendered by Americans will read in sequential order: 12/13/14.
The next time you’ll be able to write the date in the United States by simply counting up won’t come until January 2, 2103: 01/02/03. That’s 89 years from now—probably outside the lifespan of anyone reading this now but certainly a goal worth striving for. In any case, not to worry. Smithsonian has a nifty write up of upcoming dates of mathematical significance that some of us may yet live to experience.
In countries outside the U.S. where the date is rendered Day/Month/Year, this auspicious occasion passed last year on 11 December 2013: 11/12/13.