Derek turned 14 in the 1st or 2nd book. This is a more accurate answer. I messed up on the other one.
He started out as 13 at first but turned fourteen in the fourth book of the series
The climax of "The Haunting of Derek Stone: Bayou Dogs" occurs when Derek Stone confronts the evil forces that have been haunting him and his family, and he must make a difficult decision that will determine the outcome of the supernatural events. This pivotal moment brings resolution to the main conflict in the story and reveals the true nature of the haunting.
i don't think so because he finished writing in 2009 and it is now 2011. so probably no
He is 22 years old
In life with Derek Lizzie is 11 years old.
As of the 2014 MLB season, Derek Dietrich is 24 years old.
As of the 2014 MLB season, Derek Norris is 25 years old.
Derek Roy is 28 years old (birthdate: May 4, 1983).
Derek Hough is 32 years old (birthdate: May 17, 1985).
Derek Dooley is 49 years old (birthdate: June 10, 1968).
Derek Mountfield is 45 years old (birthdate: November 2, 1972).
Derek Daly is 58 years old (birthdate: March 11, 1953).