Yoga is one of the six astika darshanas. Astika is a traditional Vedic darshan. This definition comes from Shankaracharya himself.
The skeleton you see in this picture is of a man buried in Padmasana and has been excavated from Balathal (Rajasthan) He dates back to 900 BC-700 BCE. Skeleton belonged to a man who was 35-40 years old when he undertook this Samadhi. He faces north and his grave was smeared with cow dung and ash. This is typically how Yogis are buried (not cremated) in India even today. Aspects of traditional Yoga go back to at least 2700 years.