It responds to the comment "I only clicked on the article because I thought it was the age of the samples too." Age is "The length of time that a person or thing has existed." AD and BC are both absolute values from a zero point, both positive ("1 BC is year 0, 45 BC is year −44" [0]). A relative chronological dating by some phenomenological method such as radiocarbon or thermolumenescence might establish a negative date relative to some other known benchmark [1].

How might something dated from the future be found? I'm not certain, but maybe it has to do with aliens that are all the rage nowadays.

If I were 12 years old, I would have been born 12 years ago.

   2023
  -  12
   ----
   2011

If I were -12 years old, I would be born 12 years from now.

   2023
  - -12
   ----
   2035

0. https://en.wikipedia.org/wiki/Anno_Domini

1. https://en.wikipedia.org/wiki/Chronological_dating