Section 15(4) in The Assam Accounts Service Rules, 1963
(4)A Member of the Service in the cadre of Accounts Officer shall be eligible for promotion to the cadre of Assistant Director of Accounts on completion of minimum of 10 (ten) years of service in the cadre of Accounts Officer and who has attained 40 years of age on the first day of January of the year in which the promotion is considered and the Governor is satisfied about his ability, integrity and character.
