precocious

Definitions:

Prematurely ripe; too forward.
- The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. (adjective) (adj.) (adjective)
Ripe in understanding before the usual or proper time; having the mental powers developed at an early age; premature.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (adjective) (adj.) (adjective)
Precociousness, precocity.
- The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. (noun) (n.) (noun)
Precociousness.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (noun) (n.) (noun)
Having the mind developed very early: premature: forward.
- The american dictionary of the english language. By Daniel Lyons. Published 1899. (adjective) (adj.) (adjective)
Ripe before the natural time; forward in mental development; too forward.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adjective) (adj.) (adjective)
Precociously.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adverb) (adv.) (adverb)

Usage examples:

There are few details of her childhood, and no anecdotes indicating a precocious genius.
- Mary Wollstonecraft by Elizabeth Robins Pennell
Kathleen was a precocious child, with all the potentialities of youth.
- The Desert of Wheat by Zane Grey
Then she began to fear I must be ill, and took me to a doctor, who said I was much too precocious for my years, and would be better when the weather got warmer.
- My Brilliant Career by Miles Franklin