Many schools of meditation relate to “age-old tradition(s)”. But how long has humanity been meditating? It depends, I am sure, on what you mean by meditation. As a frame of mind, meditation may have been with us at least for as long as humanity as we now know it has existed. In the book Fighting Stress: Reviews of Meditation Research, Dr Svend Davanger even speculates about the meditative capacities of Neanderthal man. But what about unambiguous evidence of the systematic practice of meditation techniques?
The problem is that early texts and images are often highly ambiguous. Some have argued that the cross-legged figures on Indus Valley artefacts dating from ca. 2600 BC depict the Indian god Shiva in a precursor to Tantric Yoga (the Tantric part coming from the fact that the figure has an erect penis and very visible testicles), but this is just a very controversial interpretation. Others link their meditation practice to the earliest sacred Indian text, the Rig Veda, which dates from 1500 BC or earlier, but again this text contains no unambiguous descriptions of meditation techniques. Buddhist scriptures and Upanishadic texts from a few hundred years BC may be among the earliest cases. (But the Buddha is said to first have learned meditation from two other teachers, so he certainly wasn’t first man out. And by the way, the typical image of the Buddha sitting in the lotus posture only emerged hundreds of years after his life-time.)
In China, early forms of meditation are often linked to the Daoist classic Laozi (or Dao De Jing), which is variously dated 3rd to 6th century BC. Indeed, many of the terms later used for Chinese meditation techniques occur in this text, such as shou zhong (guarding the middle), bao yi (embracing the one), shou jing (guarding tranquility), and bao pu (embracing simplicity). But it is hard to tell from the text itself whether these were already full-fledged methods of meditation when the text was written, since the text is not very explicit, and later traditions have often adopted such names for techniques that were certainly not around at the time. Two other early Daoist texts, the well-known Zhuangzi (3rd century BC) and especially the much less well-known text Neiye (maybe as early as 4th century BC), come a little closer to describing actual techniques.
So when did people begin to meditate? We don’t know! But for some reason, meditative techniques seem to have become very prominent both in India and China in the second half of the 1st millennium BC. This corresponds to the period that laid the philosophical foundations for civilization as we know it both in India, China, and Greece.