What is the oldest tree in the world?

Oldest Living Single Tree

Big Bristlecone Pine Pinus Longaeva

This tree is 5063 years old, it is the oldest known living non-clonal organism on Earth. It is located in the White Mountains, California, Untied States. This tree was cored by Edmund Schulman, age determined by Tom Harlan. Source

Oldest Grove of Trees

Sisters Olive Trees of Noah

The Sisters or The Sisters Olive Trees of Noah are a grove of sixteen olive trees. They are estimated to be between 5,000 to 6.0000 years old. They may be the oldest non-clonal living trees in the world. The exact age of any of The Sisters has not been determined by dendrochronology (tree-ring dating), because of deterioration of the inner tree ring structures.They are located in Bechealeh, Batroun district, Lebanon.

The legend goes that "The Sisters" was the source of the olive branch returned to Noah's Ark at the waning of the Biblical Flood. The trees still produce olives, and a preservation effort has been undertaken by the non-profit organization Sisters Olive Oil, which markets oil from these olives, which you can learn more about here. Sisters Olive Oil

Oldest Clonal Trees

Pando

The roots of these trees are estimated to be between 80,000–1,000,000 years old. They are located in Fishlake National Forest, Utah, United States.  They cover 107 acres and have about 47,000 stems (average age 130 years), which continually die and are renewed by its roots. Is also the heaviest known organism, weighing 6,000 tonnes. Source