Other than Nephi himself, Amaron is the only writer on the small plates to pass them horizontally to a brother rather than vertically to a son. It would appear that he had no son to whom the records could be passed. The next date we will see in the Book of Mormon text is found in Mosiah 6:4 at the coronation of Mosiah II, noting that 476 years have passed since Lehi left Jerusalem. According to the dating we have been using, that will be the year 110 BC. Between the destruction of the "more wicked part" of the Nephites and the coronation of Mosiah, son of Benjamin, we have 156 years. It is impossible to be precise about the dating of events in between, but into a time span only 30+ years longer that we needed to trace the small plates between Jacob and Enos we have to account for the lives of no less than 7 people; Amaron, Chemish, Abinadom, Amaleki, Mosiah I, and Benjamin, and Mosiah II. Amaron and Chemish are brothers, and so we may presume that Chemish's jurisdiction over the plates was relatively short. Amaleki's life begins in the "days" of Mosiah I, and he dies during the reign of Benjamin. When we reach the date of 110 BC, Amaleki has already died.
In the plate tradition, we have five people, and four generations: Amaron/Chemish, Abinadom, Amaleki, and Mosiah II (where we have the next date, even though it is after Amaleki has given the records to Benjamin. Were the generations of equal duration, we have only 39 years for the plates to be in the hands of each of the writers (including the time to Mosiah II's coronation). This cannot be the correct distribution of years, however, as Amaleki has the plates through much of the life of Mosiah I and sees the coronation of Benjamin, which would have occurred only after Benjamin had reached an appropriate age, let's say 20 on the young side.
Since Amaleki uses the phrase "began to be old" (verse 25), a phrase we know for Nephi, Jacob, and Enos place those men in their 70's and later (see Jacob 1:9, Jacob 7:26, and Enos 1:25), I think we can be justified in giving Amaleki an age of 70+ when he dies. While that age is consistent with Nephi, Jacob, Enos, and probably Jarom, it then leaves only around 86 years to cover the time the plates were in the hands of Chemish, and Abinadom. And this would assume that Mosiah II's coronation happened immediately after Amaleki gave the plates to Benjamin, which is unlikely.
If we give at least 20 years to Benjamin after he receives the small plates, and before he gives the kingship to Mosiah II (Benjamin was old at the time, dying three years later Mosiah 6:5) then we have only 66 years for the two. While 33 years apiece is plenty, it is still much shorter than the lives of the other keepers of the small plates. It may well be that the wars they mention so frequently had some role to play in their apparently shorter lifespan.