This happened due to a strange yet interesting bug. Facebook is not even 15 years old and some users, who saw this message, are far younger than 46 years of age, The Verge reported on Friday.
The report said Facebook has not disclosed the culprit, but said that it is aware of the issue.
"We have identified this bug and the team is fixing it now so everyone can ring in 2016 feeling young again," a company spokesperson said.
The report said that the bug might be due to Unix epoch. Facebook did not confirm it.
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Many of the world's servers run on Unix -- an operating system (OS) that keeps time by counting up from zero at one-second intervals.
The date on which clock began happens to be on January 1, 1970, at midnight Greenwich Mean Time (GMT) or 46 years ago. This is known as the epoch.
Every second from that point on is known as epoch time, and this is why some gadgets mysteriously switch to December 31, 1969.