Some Chinese characters have been dated back to around 5000 years by Chinese archeologists. The oldest acceptable record of Chinese characters were traced back to Shang dynasty, the people used animal bones and tortoises shell to carved characters.
The character were collectively referred to as "Oracle Bone". It is hard to give a 'correct’ answer to this question because there are disputes over what constitutes the Chinese written language.
Some the earliest Chinese kanji charachters that have been discovered are said to have come from around 6500 BC and have been discovered recently at ancient sites in China. A couple thousand years later around 1200 BC was the discovery of oracle bone script in which scientists say is the first known example of Chinese kanji script and it was from here that modern day Chinese has evolved from.
Over the course of thousands of years and through the various dynasties and eras that ruled throughout China, the kanji has changed and new characters have been adopted. It is believed that there is at least 50,000 different kanji that is associated with Chinese script. Chinese kanji has always been known as one of the most elegant and complex writing scripts that has ever been invented. It is certainly one of the oldest scripts that is still used to this very day.