In Jain tradition, the oldest widely accepted Jain idol found in India is the Lohanipur Torso, a nude Tirthankara figure discovered near Patna (Bihar). It is generally dated to around the 3rd century BCE and is celebrated as one of the earliest archaeological evidences of Jain image worship. This is followed by later early-Jain images from Mathura/Kankali Tila (1st century BCE to 1st century CE), but the Lohanipur piece is regarded as the oldest known Jain sculpture. You can read more here