A.T. Robertson Commentary John 9:21

"but how he now seeth, we know not; or who opened his eyes, we know not: ask him; he is of age; he shall speak for himself." — John 9:21 (ASV)

But how he now seeth we know not (πως δε νυν βλεπε ουκ οιδαμεν). Concerning the third question they profess ignorance both as to the "how" (πως) and the "who" (τις).

Opened (ηνοιξεν). First aorist active indicative with single augment of ανοιγω, same form as ηνεωιξεν (triple augment) in verse 17. They were not witnesses of the cure and had the story only from the son as the Pharisees had.

He is of age (ηλικιαν εχε). "He has maturity of age." He is an adult. A regular classical phrase in Plato, etc. The parents were wholly right and within their rights.