Numbers 4:3-8:24: Why the Discrepancy in Ages for Levitical Service?

Why does the Bible give varying ages as the qualification for the Levites to perform the work of the service of the tabernacle or temple? Was the minimum twenty, twenty-five or thirty years of age? And was there a maximum age of fifty, or was it left open?

A Levite must not be younger than thirty or older than fifty years old according to Numbers 4:3, 23, 30, 35, 39, 43, 47. But in Numbers 8:24-25 the age limit was set at twenty-five and fifty. The Greek Septuagint text for Numbers 4 also reads "from twenty-five to fifty."

But the author of Chronicles set an even lower age limit of twenty, but he does not give an upper age limit (1 Chron 23:24, 27; 2 Chron 31:17; Ezra 3:8). We can probably assume that it remained at fifty. But even the chronicler recognized some change, for in the same chapter he gave the qualifying age as thirty in 1 Chronicles 23:3 and twenty in 1 Chronicles 23:24.

What can account for this vacillation from twenty, twenty-five to thirty years old as the minimum age to work in the sanctuary? No doubt the qualifying age varied from era to era depending on the needs of the sanctuary and the availability of persons. The change, except for the textual variant in the Septuagint of Numbers 4:3 (which raises the question as to what was the best and original reading of this text), occurs in the days following David's era. Apparently this reflects a change necessitated by the additional duties in the temple after it became a royal sanctuary.