There are heaps of disputes in this field, but Wikipedia does provide a reasonable consensus — that is, with lots of + or – twenty years in there… Now my idle thought was to imagine Jesus was born the same year I was: no, I am not having an attack of Messianic delusion!
OK, if he had been, the crucifixion would have happened, very aptly some Aussies may think, around 1975!
So when did the earliest Christian writings — that is, some of the epistles attributed to Paul — appear? Answer: in the early 1990s. Paul didn’t know Jesus personally, of course, Damascus road vision apart. Still, it is not hard to conceive, given my analogy, that just as plenty of people could remember Gough in, say, 1995 — he of course stayed on earth after his “crucifixion”, which makes this easier — there would have been plenty around Palestine, Galilee and Syria in Paul’s time who had connections. (Perhaps we could substitute Paul Keating for Paul in our analogy? I suspect there are similarities…)
As for the gospels, leaving aside the hypothetical “Q”, which no longer exists, the usual candidate for earliest one is Mark, which in my analogy appears around about now — 2005-2010. By 2040 you have the Gospel of John, and a whole heap of others that didn’t make it into the New Testament, such as the Didache, I Clement and the Epistle of Barnabas.