Paul Bump at Grist points out that The National Oceanic and Atmospheric Administration reported on global temperatures in October 2012 as follows:
“The average temperature across land and ocean surfaces during October was 14.63°C (58.23°F). This is 0.63°C (1.13°F) above the 20th century average and ties with 2008 as the fifth warmest October on record. The record warmest October occurred in 2003 and the record coldest October occurred in 1912. This is the 332nd consecutive month with an above-average temperature.”
He then did a quick calculation, and concluded that if you were born after April, 1985, i.e. if you are 27 or younger, you have never experienced a month with a global average temperature colder than the 20th-century average. (Obviously, you may have experienced a month at lower than local averages, though that would be rare, too; the point is about world averages.)
For a visual of the 20th century average temperature through 2011, see this NASA video: