The age of their numbering from thirty years, seems to convey very strong testimonies that a competency of wisdom and gravity were considered as necessary, before that they were numbered among the Levites.
Related Commentaries of 1 Chronicles 23:3
1 Chronicles 23:3
3 Now the Levites were numbered from the age of thirty years and upward: and their number by their polls, man by man, was thirty and eight thousand.