Numbers 8:24

8:24 “This is what pertains to the Levites: At the age of twenty-five years and upward one may begin to join the company in the work of the tent of meeting,

Numbers 9:3

9:3 In the fourteenth day of this month, at twilight, you are to observe it at its appointed time; you must keep it in accordance with all its statutes and all its customs.”