In the last 5 verses of Genesis, Joseph's 110 years is written twice. The first shows 110 years of life, while the latter shows 110 years in age. Is that just repeated for no particular reason, or are life and age two different things? The two are sometimes considered to differ by about 9 months, with life beginning at conception and age beginning at birth.
A chaism is a structure common in the Old Testament (but also found in the New Testament). It is basically text constructed in an ABCBA or ABCDCBA (or etc.) pattern. For instance, consider Luke 4
The main point that the author is trying to emphasize is generally found in the juicy center of the chiasm: in this case the emphasis is in Jesus' ministry.
It should come as no surprise at this point that I believe Gen 50:22-26 is a chiasm:
The main point, then, is Joseph's reiteration of the promise to Abraham, Isaac, and Jacob. The 110 years are repeated in order to make the chiasm more obvious.
Compare the chiasm with the text itself:
There is no reason to assume that the 9 month pregnancy period should impact the ages - either they are from conception, or they are from birth - there would be no reason to oscillate between the two.
In Genesis 50:22 the text literally says:
In v. 26, an idiomatic expression is used to say the same thing. The text of Genesis 50:26 literally says:
This is a common idiom used for expressing age in Biblical Hebrew.3 Neither expression indicates a difference in how the age should be calculated (and I cannot find any support for different calculations in scholarly literature).
The IVP Commentary offers the following information:
Several sources corroborate that 110 years of age was an ideal age of death for Egyptians.5 Overall, this information is likely repeated because it demonstrates that Joseph was a successful Egyptian official, and his age of death was a cultural confirmation of this that would have been understood by the original readers.
The context of this passage affirms that Joseph was a Hebrew, not an Egyptian, and yet emphasizes his success in both cultures. His burial was finally with the Hebrews and according to Hebrew customs rather than Egyptian practices (embalming and burial vs. mummifying).6
1 Biblia Hebraica Stuttgartensia: SESB Version., electronic ed. (Stuttgart: German Bible Society, 2003), Ge 50:22.
2 Ibid., Ge 50:26.
3 Lexical entry for בֵּן: "in expressions specifying age (→ בַּת 4): aged (so much) (MHb. JArm. Palm. Syr. Arb. Soq.): בֶּן־שְׁמֹנַת יָמִים eight days old Gn 1712, בֶּן־שָׁנָה one year old Ex 125 (1S 131 the number is missing), בֶּן־שְׁנָתוֹ (“situation specification” Landsberger JNES 8:288, → יוֹם 3, חֹדֶשׁ 2, BL 5181) one year old Lv 2312 (6 ×), בֶּן־חֲמֵשׁ מֵאוֹת שָׁנָה Gn 532, בִּן־לַיְלָה one night old, meaning grown up in one night Jon 410...."
Ludwig Koehler et al., The Hebrew and Aramaic Lexicon of the Old Testament (Leiden; New York: E.J. Brill, 1999), 138.
4 Victor Harold Matthews, Mark W. Chavalas, and John H. Walton, The IVP Bible Background Commentary: Old Testament, electronic ed. (Downers Grove, IL: InterVarsity Press, 2000), Ge 50:26.
5 Marie Parsons. "Old Age in Ancient Egypt." (Tour Egypt), retrieved from the Tour Egypt website. A search for this information will reveal numerous sources showing that 110 years was an ideal age of death for Egyptians.
6 James McKeown. Genesis: Two Horizons Old Testament Commentary series. (Grand Rapids, MI: Wm. B. Eerdmans Publishing Co., 2008), 192-193.