He started out as 13 at first but turned fourteen in the fourth book of the series
Derek turned 14 in the 1st or 2nd book. This is a more accurate answer. I messed up on the other one.
He is 22 years old
In life with Derek Lizzie is 11 years old.
Derek Rose is 22 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.
17 i believe
Derek Roy is 28 years old (birthdate: May 4, 1983).
Derek Thompson is 63 years old (birthdate: April 4, 1948).
Derek Parra is 41 years old (birthdate: March 15, 1970).
Derek Sanderson is 65 years old (birthdate: June 16, 1946).
Derek Hough is 32 years old (birthdate: May 17, 1985).