"The earliest fragment of the New Testament dates to AD 125."

P52 is early, but recent scholarship widens its date.

What's actually true

C.H. Roberts dated P52 (a fragment of John 18) to ~AD 125 in 1934, based on paleography. This is the basis for the popular claim of a 30-year gap between composition and earliest manuscript.

What gets left out

More recent paleographic work (Brent Nongbri, Pasquale Orsini and Willy Clarysse) argues a wider range, somewhere between AD 125 and AD 200. Paleography alone cannot date a hand more precisely than within about 50 years. P52 is still the earliest, but 'AD 125' is an upper-end estimate, not a settled fact.