Though it could be a pet form of some other name, it's also possible that his given name is Agee. Agee is after all a well-known surname.
James Agee was a famous American author:
http://www.pbs.org/wnet/ihas/poet/agee.html
The original ancestors of the Agee family in the USA were French Huguenots, but the exact origin of their name in
France is unknown at this time.