There are very few autobiographical references in Against Heresies. In Book Four he declares that there were many Christians in the Imperial court. Yet only the Antonine period (161 - 177 CE) would exclude that possibility.
I guess the one piece of evidence on which the whole dating of Irenaeus hangs is the famous catalogue of the Roman bishops given by Irenaeus in AH 3.3.3, Eleutherius is the last one mentioned. It is generally assumed that because Irenaeus does not mention Victor that Against Heresies was written during the Commodian period (owing to the fact that Eleutherius's reign is said to have been either 174 - 189 (or 171 or 177 - 185 or 193 according to Vatican sources).
Yet there are other possibilities. Many others beside me have wondered whether Irenaeus is actually citing the words of the Hypomnemata of Hegesippus here. In other words, the 'now' associated with Eleutherius is a reference to the list which appears as a kind of appendix of the original work written during the reign of Antoninus Pius:
From this document [i.e. the Hypomnemata], whosoever chooses to do so, may learn that He, the Father of our Lord Jesus Christ, was preached by the Churches, and may also understand the apostolical tradition of the Church, since this Epistle is of older date than these men who are now propagating falsehood, and who conjure into existence another god beyond the Creator and the Maker of all existing things.
To this Clement there succeeded Evaristus. Alexander followed Evaristus; then, sixth from the apostles, Sixtus was appointed; after him, Telephorus, who was gloriously martyred; then Hyginus; after him, Pius; then after him, Anicetus. Sorer having succeeded Anicetus, Eleutherius does now, in the twelfth place from the apostles, hold the inheritance of the episcopate. In this order, and by this succession, the ecclesiastical tradition from the apostles, and the preaching of the truth, have come down to us. And this is most abundant proof that there is one and the same vivifying faith, which has been preserved in the Church from the apostles until now, and handed down in truth.
But Polycarp also was not only instructed by apostles, and conversed with many who had seen Christ, but was also, by apostles in Asia, appointed bishop of the Church in Smyrna, whom I also saw in my early youth, for he tarried [on earth] a very long time, and, when a very old man, gloriously and most nobly suffering martyrdom,(1) departed this life, having always taught the things which he had learned from the apostles, and which the Church has handed down, and which alone are true. [AH 3.3.3-4]
I have always read this material as if Polycarp was the author of the appendix to the Hegesippus and that Eleutherius's reign might well have started as early as 164 CE. Nevertheless the idea that Clement is only citing something from an earlier writer who lived during the reign of Eleutherius is a distinct possibility.
The reason this is so important for me is that I can't help but wonder if the fourfold gospel which Irenaeus witnesses for the first time in Book Three might well have been written closer to the turn of the third century. Is it also possible that Irenaeus's information about the Marcosians is actually from hostile 'Ebionites' or Jewish Christians coming into contact with Alexandrian Christians in Palestine? In other words the prayers preserved in Aramaic (Hebrew) throughout are only so because the original witnesses spoke (and wrote) in Aramaic. The Marcosians were actually Greek speaking (as seems to be indicated by the other statements of Irenaeus).
Under this scenario, the Ebionites made references to people like Clement of Alexandria as marqiyone and these original reports developed in two ways - (a) as Irenaeus's testimony regarding the 'Marcosians' (owing to his efforts to translate the original material and then (b) Clement of Alexandria's increasingly frequent allusions to 'those of Marcion' (starting in Book Two of the Stromata but more frequently in Book Three where they are almost a caricature of Clement himself - i.e. Platonizing ascetics). Gregory Nazianzus and many other educated fourth and fifth century writers realize that the two reports go back to one original sect and fuse them together.
The main idea here would be that Clement of Alexandria fled Alexandria to Jerusalem during the Commodian period, writing throughout the reign of the son of Marcus Aurelius and that Irenaeus only began writing the material which would become Against Heresies in the latter half of the rule of Commodus but imperfect knowledge of the two terminologies.
