Regarding the census in verses 23-24, see chapter 21.
David did not number those below twenty years of age: Verses 23-24 are loosely connected to the preceding verses. The beginning of verse 23 in the Hebrew reads “And David did not take their number from twenty years old and under.” The pronoun “their” has no clear antecedent. The natural antecedent is “the leaders of the tribes of Israel,” but clearly the reference is to all Israel and not just the leaders. Neither Revised Standard Version nor Good News Translation (nor most other translations) translates the Hebrew pronoun for “their.” The Hebrew text does not qualify David as “King” here in verse 23, but does so in verse 24. However, in some languages it may be advisable to follow the example of Good News Translation, which adds the word “King” in this verse. This whole clause may be rendered “King David counted only those who were twenty years old or older.”
For the LORD had promised to make Israel as many as the stars of heaven: See Gen 15.5; 22.17; 26.4. This clause explains why David did not take a census for those people under the age of twenty, so the Hebrew connector rendered for is significant. New International Version uses the conjunction “because.” But the logic here may not be clear to all readers. According to Num 1.3, Moses was told to take a census of every male twenty years old and older who was able to serve in the military. The LORD had promised is literally “the LORD had said,” but most English versions as well as La Bible du Semeur use the verb “promised” because of the context. Bible en français courant has the verb “announced.” Israel may be rendered “the people of Israel” (Good News Translation) or “the Israelites” (Bible en français courant, Biblia Dios Habla Hoy).
New Century Version reverses the order of the two halves of this verse, saying “The LORD had promised to make the Israelites as many as the stars in the sky. So David only counted the men who were twenty years old and older.”
Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on 1-2 Chronicles, Volume 1. (UBS Helps for Translators). Miami: UBS, 2014. For this and other handbooks for translators see here .