It means that a person can be an official.

"To say that a person can be an official" means that this person has the ability and will be a leader in the future.

This passage reminds me of my grandmother:

My grandmother is a very talkative person, who enjoys nagging all day. When I go to school, I often take my classmates home to play, because my parents are busy with work and there are few people at home. Of course, this is also my grandmother's request.

A boy is good at talking, and around my grandmother, there are long and short, and he will please her very much. Not only have strong language communication skills, but also do things appropriately. Later, my grandmother said, "You will be an official when you grow up, because you are the material for being an official." . It means: "your ability is great, and your future career is bright."

To say that a person can be an official is actually to be a leader after entering the officialdom. It can also be understood as a very capable person.