This enumeration takes the form of something like a census. Benjamin would take a census over one thousand years later when he was dealing with a combined population of Nephites and Zarahemlaites that had experienced significant defections to the Lamanites. (See commentary accompanying Mosiah 2:2, 6:1–2.) He had excellent political reasons for taking a census, as it would otherwise be difficult to know how many people were included in the Zarahemla polity.
The Jaredite case strongly suggests a similar population mixing and enlargement. It would be a relatively simple matter for the original twenty-four males to enumerate their posterity. The very fact of the count tells us that something else has happened. I posit that, as with Benjamin, it is difficult to determine who now calls themselves Jaredites; and the simplest explanation for that difficulty is the infusion of “others” already living in the area.
Like the Nephites, the Jaredites had something that gave them priority in governance over peoples with whom they merged, but it was probably not cultural dominance. They had to learn new geography, climate, plants, animals, and farming methods. To learn those skills, they had to depend on those who had already figured out how to live in the land. (See “Excursus: Ethnohistory and the Book of Mormon,” following 1 Nephi 18.)
Symbolism: The numbers given are too neat to plausibly be actual counts. There are twenty-four adult males (twice twelve). Jared had four sons and twelve total children. All of these numbers are important in either the Bible (twelve) or Mesoamerica (four). In other words, the only numbers given have symbolic meaning. (See Helaman, Part 1: Context, Chapter 4, “The Meaning of Numbers: Counts and Estimates in the Book of Mormon.”)
Reference: The phrase “began to be old” is apparently a Nephite stock phrase meaning “on his deathbed. (See commentary accompanying Jacob 1:9.) Its presence in the Jaredite record provides further evidence of its transmission through Mosiah2’s translation and Moroni’s redaction; in either case, the Nephites allowed their language to influence the text. In this case, the consistency of “began to be old” in the text but its absence from Joseph Smith’s lexical climate suggests that he translated it with some faithfulness to the underlying text.