The bottom line is that there is some degree of uncertainty regarding what Irenaeus meant. Was it Domitian or Domitius (Nero) that Irenaeus was referring to? Where the book of Revelation is included in the Syriac versions it is referred to as "The Revelation which was made by God to John the evangelist in the island of Patmos, into which he was thrown by Nero Caesar."
At any rate, here is what Eusebius quoted:
Irenaues did not speak from firsthand experience, but heard this thought from Polycarp. Polycarp allegedly knew John personally.
"In this persecution [of Christians under Domitian], it is handed down by tradition, that the apostle and evangelist John, who was yet living, in consequence of his testimony to the divine word, was condemned to dwell on the island of Patmos. Irenaeus, indeed, in his fifth book against the heresies, ...speaks in the following manner respecting him: 'If, however, it were necessary to proclaim [the name of the Anti-Christ], ... it would have been declared by him who saw the revelation, for it is not long since it was seen, but almost in our own generation, at the close of Domitian's reign." (Eusebius, III, XVII)
"Chapter XXII.-The Thirty Aeons are Not Typified by the Fact that Christ Was Baptized in His Thirtieth Year: He Did Not Suffer in the Twelfth Month After His Baptism, But Was More Than Fifty Years Old When He Died."
"...but they mentioned a period near His real age , whether they had truly ascertained this out of the entry in the public register, or simply made a conjecture from what they observed that He was above forty years old, and that He certainly was not one of only thirty years of age. For it is altogether unreasonable to suppose that they were mistaken by twenty years, when they wished to prove Him younger than the times of Abraham. For what they saw, that they also expressed; and He whom they beheld was not a mere phantasm, but an actual being of flesh and blood. He did not then wont much of being fifty years old ..."If Irenaeus did imply the book was written in 96 A.D., how reliable is his dating anyway? Saying Jesus died at fifty years of age is a similar type of dating error that Irenaeus proposed.
And unto the angel of the church of the Laodiceans write; These things saith the Amen, the faithful and true witness, the beginning of the creation of God; (Rev. 3:14).Laodicea was destroyed by a mighty earthquake in 60 B.C. It was hit again in 65 AD.
But the court which is without the temple leave out, and measure it not; for it is given unto the Gentiles: and the holy city shall they tread under foot forty and two months. (Rev 11:2).