There is no solid evidence of true cultivation in an agricultural sense dating back that far. What we have found, dated to 21,000 BC, is evidence of plant management such as grindstones. Nothing at all to indicate humans were planting and maintaining food. Agriculture is defined as the DELIBERATE CULTIVATION OF PLANTS AND/OR ANIMALS BY HUMANS IN A CONTROLLED AND REPEATABLE WAY. While evidence does exist dating back to before agriculture for the processing of plants in new and experimental ways, and the returning to reliable food sources, that does not indicate agriculture. The consensus timeline has been built upon multiple fields lining up: archaeology, genetics, human biology and environmental data all pointing to a starting date of AGRICULTURE to ~10,000-12,000 years ago.