Answer

Bhagwan Rishabhdev (Rishabhanatha / Adinath) is traditionally said to have lived for 8,400,000 purva years. ( jainknowledge.com)

Explanation

In Jain tradition, a purva is an extremely vast unit of time, so this indicates an unimaginably long lifespan. ( jainpedia.org)

Takeaway

So, the commonly accepted Jain answer is: 8,400,000 purva years.