«إِنَّهُ قَرْنُ مِحَالِكَ وَقَرِينُ جِدَالِكَ»
He is a match for your contest and an equal in your disputation.
Qarn denotes a capable opponent, while qarīn means a companion or peer; jidāl is disputation. The similar sounds of qarn and qarīn reinforce the elder's confidence and give the line a sharp rhetorical rhythm.
Importantly, this is a character's assertion, not yet a demonstrated fact. The assembly still has good reason to ask for a test, and the narrative uses this tension to move the action forward.
Practical criterion: Actual performance on a demanding composition, rather than reputation, will decide the claim.