Precocious

Apr 2

[pri-koh-sh_uh_ s]

Definition:

Unusually advanced or mature

Example of usage:

While the rest of the class was struggling with their work, the precocious child had finished already and was causing a ruckus because he was bored.

Comments:

This is definitely one of those words that is very descriptive of what you’re trying to say. You can try to explain what you mean with this word in many more words, but this word displays much more brevity. And that is always good.