According to Jain Dharma:

• The truth (tattva) and dharma taught by the Tirthankaras are considered anādi – beginningless and eternal.
• So, from the Jain viewpoint, Jain Dharma is not “started” at a particular time like a new religion; it is the re‑manifestation of the eternal path shown again and again by different Tirthankaras in every time‑cycle (kālchakra).

In terms of recorded human history:

• Modern historians usually speak of religions like ancient Vedic tradition, Judaism, etc. when they ask “oldest religion”.
• Jain tradition, however, teaches a much more ancient spiritual lineage of 24 Tirthankaras in the current time‑cycle, starting from Bhagwan Rishabhdev (Adinath), long before recorded history.

So:

• From a Jain spiritual perspective:

Dharma (and specifically the Jain path of ahimsa, aparigraha, and self‑realisation) is eternal and therefore has no beginning – so you cannot truly say “which is first”; it is sanātan (anādi–ananta).

• From a Jain traditional claim in the context of world religions:

Jains often say that Jain Dharma is among the most ancient still‑living religions, with roots going far earlier than the historical period of Bhagwan Mahavir.

You can read a bit more about the antiquity of Jainism here: