Definition of "precocious"

Now those abominations whom you call precocious boys—your little pet monsters, doctor!—and who can wonder that the world is what it is? when it is full of them—as they will have no divine time to look back upon in their own lives, how can they believe in innocence and goodness, or be other than sons of selfishness and the Devil?

1859, George Meredith, chapter 15, in The Ordeal of Richard Feverel. A History of Father and Son. […], volumes (please specify |volume=I to III), London: Chapman and Hall

Scotland’s most encouraging early source of an attacking threat was Andrew Robertson as the precocious left-back charged forward to good effect on a couple of occasions.

2014 November 14, Stephen Halliday, “Scotland 1-0 Republic of Ireland: Maloney the hero”, in The Scotsman‎

Both groups, also, have already evolved precocious (intracapsular) spore germination.

1992, Rudolf M[athias] Schuster, The Hepaticae and Anthocerotae of North America: East of the Hundredth Meridian, volume V, New York, N.Y.: Columbia University Press, page 5

Mary: Even though the sound of it is something quite atrocious / If you say it loud enough you'll always sound precocious.

1964, Sherman Brothers (lyrics and music), “Supercalifragilisticexpialidocious”, in Mary Poppins, Walt Disney