Learn English – word to describe a person who is always curious

single-word-requestssynonyms

Is there a word or phrase for describing a person who is always curious?
Curiosiac?

Example usage (as requested by a comment):

The boy is such a ___, he asks questions all the time!

UPDATE

I appreciate all your answers, but my question was if there was any word – a noun – to describe a person of that kind, e.g. maniac, lunatic, weirdo, nerd, etc.

Best Answer

Inquisitive, defined by Dictionary.com

  1. given to inquiry, research, or asking questions; eager for knowledge; intellectually curious:

"an inquisitive mind"

  1. unduly or inappropriately curious; prying