If you really want to get a sense of how old Yoga is look at the sutras of Pantanjali.
The Yoga Sūtras of Patañjali which are the foundational text of classical yoga philosophy are around 2000 years old.
They fell into relative obscurity for nearly 700 years from the 12th to 19th century and then made a comeback in late 19th century.
During the 20th century, modern practitioners of yoga elevated the sutras to common use translating it into various languages so it could be understood around the world.
Sutra in sanskrit means a rope or thread that holds things together.
The themes of the sutras are universal to the human consciousness and a way of mindful living and are still very relevant today, despite their age. As Patanjali writes, all that matters is that we begin here and now and commit to living and practicing with greater self-awareness and presence.
The sutras show you the lineage of yoga to help you get a better understanding of the history behind certain poses and sequences. From that you earn a certain respect and understanding of the asanas. They remind you of the true purpose of your practice and the sutras talk about the philosophy and helps you to understand the barriers to living a happy and fulfilled life and essentially on how to begin to live your yoga.
I want to end with a verse I found translated. I think it’s amazing how philosophy like this can withstand the test of time and still be as relevant today as it was around 2000 years ago.
“We are not going to change the whole world, but we can change ourselves and feel free as birds. We can be serene even in the midst of calamities and, by our serenity, make others more tranquil. Serenity is contagious. If we smile at someone, he or she will smile back. And a smile costs nothing. We should plague everyone with joy. If we are to die in a minute, why not die happily, laughing? (136-137)”
– Sri S. Satchidananda, The Yoga Sutras