Interestingly Iraeneus also says that Jesus died of old age and not at 30 years.
He did not mean that in a literally, chronological sense.
Its funny on of the grand pillars of christian doctors and history has his facts totally wrong.
No, he had his facts in agreement with the other sources on the literal age of Jesus. His point was that Jesus encompassed all the ages of human life in his span of time in this world, and that he was between the age of 30 and 50--old enough to be "of age" to act as a teacher.
Ireneaus knew what the written Gospels said. He was one of the first to name them as being the four recognized as canonical in later times.
The Gospels could not possibly be either more or less in number than they are. Since there are four zones of the world in which we live, and four principal winds, while the Church is spread over all the earth, and the pillar and foundation of the Church is the gospel, and the Spirit of life, it fittingly has four pillars, everywhere breathing out incorruption and revivifying men. From this it is clear that the Word, the artificer of all things, being manifested to men gave us the gospel, fourfold in form but held together by one Spirit.
That's from the same work you referred to: Against Heresies.