PRECOCIOUS

[adjective] - (of children) showing unusually early mental development or achievement, or (esp. disapproving) behaving as if you are much older than you really are The child's precocious ability to play chess is astonishing.At the precocious age of 29 she was made a professor of philology.(esp. disapproving) He's such a precocious little brat that none of the other children want to play with him.