2 The production, again, of the Duodecad of the Æons, is indicated by the fact that the Lord was twelve years of age when He disputed with the teachers of the law, and by the election of the apostles, for of these there were twelve. The other eighteen Æons are made manifest in this way: that the Lord, [according to them,] conversed with His disciples for eighteen months after His resurrection from the dead. They also affirm that these eighteen Æons are strikingly indicated by the first two letters of His name [᾿Ιησοῦς], namely Iota and Eta. And, in like manner, they assert that the ten Æons are pointed out by the letter Iota, which begins His name; while, for the same reason, they tell us the Saviour said, “One Iota, or one tittle, shall by no means pass away until all be fulfilled.”
Source: Adversus haereses (New Advent)