In Jainism, Rishabhdev (Adinath) is counted as the first Tirthankar. His birth is described in the cosmic time cycle, not in our ordinary Gregorian years. Jain texts place his life in the very ancient beginning of the current half-cycle (kalpa) of time, amounting to countless millions of years ago. Because time in Jain cosmology is counted in kalpas and other cosmic units, there isn’t a fixed “how many years ago” date like we use for historical figures.

If you’d like, I can explain how Jain time is measured (kalpas, yugas, etc.) in simple terms.