Number 4:1

"The LORD spoke to Moses and Aaron, saying, “Take a census of the sons of Kohath from among the sons of Levi, by their clans and their fathers' houses, from thirty years old up to fifty years old, all who can come on duty, to do the work in the tent of meeting." Num. 4:1

Maybe Jesus started is 'public' ministry at 30 years of age because he was to be the Greatest of all people to execute a priestly ministry for man and God.

Just an observation,

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