Identifying the age of a speaker using speech recognition
Have a look at the acoustic scale website for some inspiration

http://www.acousticscale.org/wiki/index.php/Main_Page

You can estimate age based on a combination of vocal tract length (vtl) and pitch. Both of these attributes can be extracted from vowel sounds. Children will have short vtls and high pitch, adult males will have low pitch and long vtl, adult women will have fairly long vtls and higher pitch. Dwarfs can have short vtls and low pitch. The castrato will have long vtl and high pitch.