There are no minimum or maximum ages for obtaining a medical certificate. Any applicant who is able to pass the exam may be issued a medical certificate.
However, since 16 years is the minimum age for a student pilot certificate, people under 16 are unlikely to have practical use for an airman medical certificate.
Page Last Modified: 04/16/13 07:33 EDT
This page can be viewed online at: http://www.faa.gov/licenses_certificates/medical_certification/faq/response7/