In my practice, I must get this question from curious patients at least once a week. My answer is usually "it depends on who you ask". It's commonly held knowledge that about 3,000 years ago, some scholars in China decided to write down all the meridian theory and point locations and make it into a comprehensive system of medicine.
But if you ask an anthropologist, you may hear about the interesting tattoo markings on Otzi, the 5,300 year old mummified "iceman" found in the Austrian Alps in 1991. There's a lot of compelling evidence that what we call acupuncture may have existed long before it became Chinese Medicine: