i agree, visual age grading is used because it does yield some results based on facts known about how people age in general. human judgment is still required. The fields of bioinformatics, physical anthropology, and forensics lend credence to visual age grading. Here are a few somewhat topical research articles on the subject.
Aspects of Age Variation in Facial Morphology Affecting Biometrics
Patterson, E.; Sethuram, A.; Albert, M.; Ricanek, K.; King, M.
Biometrics: Theory, Applications, and Systems, 2007. BTAS 2007. First IEEE International Conference on
Volume , Issue , 27-29 Sept. 2007 Page(s):1 - 6
Digital Object Identifier 10.1109/BTAS.2007.4401953
Summary:There is a great degree of variation that occurs in the face during aging of adults that will affect outcomes for face- based biometric systems. These changes have been studied sporadically in anthropological research and have received even less attention in biometric-related literature. This paper presents a summary of recent research that spans biometric, forensic, and anthropologic literature in an attempt to unify a variety of findings related to adult aging, discusses work in synthesizing images of aged faces and its relation to the anthropological findings, and also presents work demonstrating a need for further study in this area to improve face-based biometric techniques. Only age-invariant or aging-aware methods will have the best success in longer stretches of time.
Reliability of the methods applied to assess age minority in living subjects around 18 years old: A survey on a Moroccan origin population .
Forensic Science International , Volume 154 , Issue 1 , Pages 3 - 12
P . Garamendi , M . Landa , J . Ballesteros , M . Solano
Facial Soft Tissue Depths in Craniofacial Identification (Part II): An Analytical Review of the Published Sub-Adult Data*
Journal of Forensic Sciences
Volume 53, Issue 6, Date: November 2008, Pages: 1273-1279
Carl N. Stephan, Ellie K. Simpson