The age of the Bennett has been an enigma and the subject of several attempts to determine the age. As reported in Madroño, the tree was cored in the 1930s by Glock and he estimated the age as about 3,000 years old. The tree was cored again in 1989 by Peter Brown from the University of Arizona Tree Ring Lab at the request of the current owners of the Bennett, Save the Redwoods League. His estimate based on a short sample was the age was also almost 3,000 years. During this coring it was discovered that rotten wood was reached about 2 feet (0.61 m) into the tree and that the tree was also partially hollow. As a result there will never be a definitive result from a complete core sample.
The naturalist Clarence K. Bennett for whom the tree is named believed the tree to be over 6,000 years old. His conclusion was based upon extrapolations of measurements taken either from core samples or cross-sections of nearby trees. An example is a cross-section from a downed juniper about 200 feet (61 m) away which was 16 inches (41 cm) in diameter and 800 years old. About 10 miles (16 km) away is the Scofield Juniper stump which is about 6 feet (1.8 m) in diameter and 2700 years old by ring count. A major issue with the extrapolation method is that the Bennett has some access to water in a drainage which is unusual in this area for junipers.
The Bennett Juniper's height is 78 feet (24 m) feet with an average crown spread of 56 feet (17 m). The diameter at breast height (4.5 feet (1.4 m) above ground) is 12.7 feet (3.9 m). This gives it a total of 573 points by the American Forests formula for measuring "Big Trees", and by that measure the Bennett is the largest juniper of any type listed in the National Register of Big Trees.
According to wikipedia