'Age' in the Bible

After David had reached old age, and had completed his reign, he set his son Solomon as king over Israel.

Since, according to David's final instructions, the list above contains the total number of descendants of Levi from the age of 20 years and upward,

David did not complete a census of those younger than 20 years of age, since the LORD had said he would make Israel as numerous as the stars of heaven.

He died at a good old age, having lived a full life, replete with riches and honor, and with his son Solomon reigning in his place.