The oldest tree is believed to be a Great Basin bristlecone pine tree named Methuselah, located in the White Mountains of California, USA. Methuselah is estimated to be over 4,800 years old, making it one of the oldest known living organisms on Earth. This ancient tree has survived harsh environmental conditions and continues to thrive in its remote mountainous habitat. Its exact location is kept secret to protect it from potential harm. **

It is difficult to determine the oldest religion definitively as the origins of many religions are shrouded in antiquity. However, Hinduism is often considered one of the oldest religions in the world, with roots dating back over 4,000 years. Other ancient religions include Zoroastrianism, which dates back to around 3,500 years ago, and ancient Egyptian religion, which also has a long history. **

The oldest author is believed to be Jim Henry, who published his first book, "In a Fisherman's Language," at the age of 98 in 2011. Henry began writing while serving a life sentence in prison and continued to pursue his passion for writing after his release. His debut book received critical acclaim and he went on to publish more works in his later years. **

The Gospel of Mark is considered the oldest of the four canonical Gospels in the New Testament. It is believed to have been written around 70 AD, making it the earliest Gospel to be written. The Gospel of Mark is also the shortest of the four Gospels and is thought to have been a primary source for the Gospels of Matthew and Luke. **

The oldest known civilization is the Sumerian civilization, which emerged in the region of southern Mesopotamia (modern-day Iraq) around 4500 BCE. The Sumerians are credited with developing the first known system of writing, known as cuneiform, as well as creating some of the earliest known examples of complex urban societies, with advanced architecture, agriculture, and trade. Their contributions to human history laid the foundation for many aspects of modern civilization. **

The oldest religious song is believed to be the "Hurrian Hymn No. 6," which was discovered in the ancient city of Ugarit in modern-day Syria and dates back to around 1400 BCE. This hymn is written in the Hurrian language and is dedicated to the goddess Nikkal. As for the oldest religious music in the world, the Sama Veda, one of the four Vedas of Hinduism, is considered to contain some of the oldest religious music. The Sama Veda consists of a collection of hymns and chants that were used in ancient Vedic rituals and is believed to have been composed around 1500-1200 BCE. **

The oldest existing democracy is generally considered to be the United States. The U.S. Constitution, which established the framework for the country's democratic system, was ratified in 1788. Since then, the United States has held regular elections and maintained a system of checks and balances among its branches of government, making it one of the longest-standing democracies in the world. **

The oldest YouTube comment is believed to be from a user named "cobaltgypsy" on a video titled "Me at the zoo," which was the first video ever uploaded to YouTube on April 23, 2005. The comment simply says "Interesting..." and was posted on the same day the video was uploaded. This comment has become iconic in YouTube history as it was one of the first interactions on the platform. **