In a thread last week about whether the apostle John died as a martyr, the issue of the timing of his death came up. It's an important subject in many contexts, such as when the canon of scripture was closed and when Revelation was written, which in turn is significant in disputes over eschatology. The timing of John's death also has a lot of relevance to liberal and skeptical theories about alleged changes in Christian belief that supposedly occurred during the closing decades of the first century. If somebody like John was still alive and prominent in church affairs until the late first or early second century, that creates some major problems for many nontraditional views of early Christianity. Here are a few posts I've written on how long John lived and how influential he was in the closing years of his life:
Mary And John As Examples Of Sources Of Information On Jesus' Background
The Apostle John's Long Lifespan
When Was Revelation Written?
The Hitchcock/Hanegraaff Debate On The Date Of Revelation