The oldest piece of paper known to date is made mostly from cotton rags.
That oldest piece of paper that was found is thought to date from around the time of AD 150 and was discovered in Wuwei in China's Gansu province.
There could be some more older papers as well but that seems to be the oldest.
However there was another paper found which is a fragment of a map that was found in Fangmatan, to the 2nd century BCE.
It would be interesting if there was more paper found that is even older but since paper does not hold up too well it's unlikely that older paper will be found.