b. Of a person (now esp. a child): prematurely developed or showing an unusual degree of advancement in some faculty, ability, or proclivity; (hence, of attributes, behaviour, etc.) indicative of such development.
Now freq. mildly derogatory, with connotations of overconfidence, self-assertiveness, or pretension.

1678 R. CUDWORTH True Intellect. Syst. Universe I. iv. 388 However it hath been of late so much decried..by..Precocious and Conceited Wits also, as Non-sence and Impossibility. 1704 S. LOWTH 68 If it be proved, as the Precocious Reflector concludes, that Mr. Dodwell was no member of the Church of England, [etc.]. 1799 Public Characters of 1798 32 The future historian..will dwell with ardour on the early promise of genius, the precocious talents of the boy. 1829 E. BULWER-LYTTON Devereux I. I. v. 46 We were all three..precocious geniuses. a1863 THACKERAY Christmas Bks. (1872) 19 His ‘Love Lays’..were pronounced to be wonderfully precocious for a young gentleman then only thirteen. 1868 E. EDWARDS Life Sir W. Ralegh I. xv. 299 She was somewhat precocious in love matters. 1929 W. DEEPING Roper's Row ix. 96 He always was a precocious little scut. 1952 J. STEINBECK East of Eden xxxvi. 421 Adults were impressed with what seemed to them a precocious maturity. 1994 Q Aug. 67/2 ‘When you're in the public eye,’ he sighs, ‘people like to make fun of you.’ Presumably for being a chubby, precocious tot,..and a member of an over-toothy, goody two-shoes family.

If you say it loud enough, you'll always sound precocious...