Documents in my possession:
American and French birth Certificates
My brother was born in Evereaux, France while my parents (in the Air Force) were stationed there. At that time, French law required that he maintain dual citizenship (French and US) until the age of 21, when he must denounce one of the citizenships. He was required to have 2 birth certificates. If at age 21, he didn't make a selection, the French citizenship would automatically be revoked.
*Source: Linda Carol Graves Walker