Great Zimbabwe is the oldest stone building on Earth. The hundreds of similar structures spread across Zimbabwe and northeast South Africa, were built by Black Africans 15,000 years before any stone building was erected in Europe.
When Europeans first saw these they made great efforts to claim they were built by Asiatics. This was the standard view until their unwarranted claim fell apart under inspection.
Stone ruins cannot be dated by the stone alone but require organic material within the stone to date them, such as mortar to bind the stones.
This is why Great Zimbabwe and the Great Pyramids cannot be dated using any archaeological method, they DO NOT use any mortar or organic material in their construction.
The patina that remains on the rock is unreliable because they could derive from recent fires which commonly occur in these areas during dry season.
The best way to date them is to realize that they were mostly built using astronomical alignments.
18,000 years old is actually a very modest date, for according to modern White archaeologists, such as Johane Heine and Tellinger, these southeast African stone castles were built over 100,000 years ago and are the oldest stone buildings on Earth.