כִּ֣י בְדִבְרֵ֤י דָוִיד֙ הָאַ֣חֲרֹנִ֔ים הֵ֖מָּה מִסְפַּ֣ר בְּנֵי־לֵוִ֑י מִבֶּ֛ן עֶשְׂרִ֥ים שָׁנָ֖ה וּלְמָֽעְלָה׃
Denn nach den letzten Verordnungen Davids wurden die Söhne Levis ab zwanzig Jahren gezählt.
Rashi on I Chronicles
the sons of the Levites were numbered from twenty years old and upwards Then David established these watches, so that when Solomon his son would come, they would be prepared for him.