David P. Barrett and Phillip Wesley Comfort note dating of earliest known Gospel manuscripts.
David P. Barrett and Philip Wesley Comfort, The Text of the Earliest New Testament Greek Manuscripts (Wheaton, IL: Tyndale House, 2001), 23
The earliest known New Testament manuscript is P52, a fragment of John's Gospel. The papyrus fragment was dated by various paleographers to the first half of the second century--even to the first quarter (see discussion under P52). . .no one would commit to a date earlier than A.D. 125. In the end, C.H. Roberts dated it to "the first half of the second century." This conservative dating allows for a larger time gap between the autograph and copy, but there is nothing unreasonable about assigning a date of A.D. 100-125 for P52. If the Fourth Gospel was written in the 70s or 80s, then we have a manuscript fragment twenty years removed from the autograph. No other New Testament manuscript has been assigned a date prior to A.D. 150 with any kind of consensus.