It isn’t clear why face recognition ability should mature so much later in life than other abilities. Research published in the journal Cognition by a team that includes Laura Germine of Harvard University and face recognition researchers Ken Nayayama and Bradley Duchaine has been discussed in ScienceNews. One of the tests used in the study is the Cambridge Face Memory Test. The original paper can be viewed in full text, not behind a paywall.
Bower, Bruce Face memory peaks late, after age 30: Finding challenges view that all mental faculties max out in young adulthood. ScienceNews. January 1st 2011. Vol. 179 No. 1 p.16.
Germine, Laura T., Duchaine, Bradley, Nakayama, Ken Where cognitive development and aging meet: Face learning ability peaks after age 30. Cognition, Volume 118, Issue 2, February 2011, Pages 201-210. http://www.sciencedirect.com/science/article/pii/S0010027710002611