A.Q. Afnán suggests that based on extensive family correspondence examined by him, the Báb began to work in His uncle’s office at the age of ten, and it was at the age of fifteen—the age of maturity in Islamic law—that He moved to Bushihr.
The same information is provided by the Báb Himself in the Kitab-i-Fihrist:
“After My childhood had passed, by the will of God, I began the occupation of commerce as this was decreed by God, and I commenced this from the age of ten.”
(Provisional translation, Footnotes to ‘The Báb in Shiraz, An Account by Mírzá Habíbu’lláh Afnán’, provided by Ahang Rabbani)