There is no specific minimum age mentioned in the Bahá'í teachings at which girls may marry.

Shoghi Effendi said :
"There is no specific minimum age mentioned in the Bahá'í teachings at which girls may marry."

He noted
"In dealing with people who are still backward in relation to our civilized standards...we must not be too strict in enforcing our opinions on peoples still living in primitive social orders."

http://bahai-library.com/uhj_reconciliation_apparent_contradictions#s3