A centenarian is a person who has reached the age of 100 years. Because life expectancies worldwide are below 100 years, the term is invariably associated with longevity. In 2012, the United Nations estimated that there were 316,600 living centenarians worldwide. As world population and life expectancy continue to increase, the number of centenarians is expected to increase substantially in the 21st century. According to the UK ONS, one-third of babies born in 2013 in the UK are expected to live to 100.