Aside from textual difficulties (there are many differences between the most ancient texts on this matter) we are faced with the question of how to explain these exceptionally long life spans (all these individuals were at least 65 when their first child was born, and most lived for up to 1,000 years!).  The problem is compounded by the fact that if we put the various data together, we come up with a date for the creation of Adam (about 4004 BC) which would be even more recent if we assumed normal life spans for his descendants!

Wenham, after reviewing various options, concludes that no adequate explanation is available at present.  McKnight (DOT:P, art. ‘Seth’) wryly notes:

‘there are no successful attempts at explaining the ages of the antediluvians other than that each one met the same end.’

Various theories have been put forward.  They cluster around two possibilities: either that the numbers are to be taken more or less as they stand, or that they are inflated in some way.

A. Literal interpretations

1. The traditional view is that the numbers are to be taken literally, without gaps, and that the earth is, accordingly, just a few thousand years old.  Howe and Geisler (When Critics Ask) offer the following points in favour:

‘(1) First of all, life was later shortened to 120 years as a punishment from God (Gen. 6:3). (2) Life span decreased gradually after the flood from the 900s (Gen. 5) to the 600s (Shem 11:10–11), to the 400s (Salah 11:14–15), to the 200s (Rue 11:20–21). (3) Biologically, there is no reason humans could not live hundreds of years. Scientists are more baffled by aging and death than by longevity. (4) The Bible is not alone in speaking of hundreds of years life spans among ancients. There are also records from ancient Greek and Egyptian times that speak of humans living hundreds of years.’

2. As a variation on the first option, Kaiser (Hard Sayings of the Bible) thinks that the ages Adam and others are to be understood literally.  The long life spans reflect ‘the fact that the effects of the Fall into sin had not yet affected human generative powers as seriously as they have more recently’.  However, he takes an ‘age-day’ view of Genesis 1, and thinks that the sons attributed to Adam and others may have been between one and six generations away.  (In support of this latter point, Kaiser points to Gen 46:18, where Zilpah is said to ‘bear’ her grandchildren, and Gen 46:25, where the same is said of Bilhah).  Kidner takes a similar view.

Writing in the Apologetics Study Bible (art. ‘Numbers in the Bible’), Kirk Lowery writes:

‘Some have suggested that environmental conditions could explain it; others suggest mankind’s closer proximity to its original sinless estate explains it. We just don’t know how to explain the apparently impossible life spans. What we have is a witness (the Bible) that has proved trustworthy too often to dismiss.’

According to Jonathan McClatchie, there are some frequently-overlook problems with the literal interpretation.  For example, the note that “Abraham breathed his last and died in a good old age, an old man and full of years,” (Gen 25:8), does not ring true if the ages of his ancestors are to be understood literally.  In fact, four of them (Shem, Arphaxad, Shelah, and Eber) would still have been alive when Abraham entered Canaan; indeed, the two last-named would have outlived Abraham.  But ‘the text treats these men as respected ancestors, not contemporaries. There is no hint that these men were living at the same time as Abraham, and the narrative would not make sense if they were’ (Craig Olson).  The age given for Abraham as his death (175) can scarcely be described as ‘old age’ in the light of the ages of his ancestors (Shem (600), Eber (464), Methuselah (969), Noah (500), Enoch (365), Terah (205)).

McClatchie adds that Abraham’s protest that he is too old, at 100, to bear children (Gen 17:15-19) does not make sense if his own father, Terah, bore him at the age of 130.  Still less does it make sense if Noah fathered children at the age of 500.

Sarah, likewise, expressed incredulity at the prospect of bearing a child at the age of ninety Gen 18:11-15.  The narrative clearly suggests that the birth of Isaac was of the nature of a miracle, a deviation from the norm.  This suggests that the extreme ages (at death and at the time of bearing children) given for the antediluvians are not to be taken literally.

Turning to the New Testament, we do not need to accuse Matthew of error or blinder when he arranges his genealogy in three groups of 14, totalling 42 generations from Abraham to Christ.  To put it bluntly, Matthew is manipulating the maths in order to make a theological (and memorable) point.

B. Non-literal interpretations

McClatchie notes that according to archaeological evidence dating back to 9000 BC, the maximum age for humans has been 70 or so, with the majority dying much younger.

1. Some think that the years of Genesis 5 were much shorter than ours.  Perhaps we should understand them as months, rather than years.  Adam’s age of 930 years would then become a more manageable 80-odd years.  The trouble is that according to this theory Nahor would have fathered Terah at the age of two, rather than 29 (Gen 11:24)!

4. According to W.H. Green, the numbers cover multiple generations, with long gaps in the genealogy.  In this case the numbers might indicate the lifespan of the family, rather than the lifespan of the individual (Kidner).  But this would not work for Enoch, of course, who was ‘taken up to heaven’.  Howe and Geisler state a number of valid objections to this interpretation:

‘First, some of these names (e.g., Adam, Seth, Enoch, Noah) are definitely individuals whose lives are narrated in the text (Gen. 1–9). Second, family lines do not “beget” family lines by different names. Third, neither do family lines “die,” as each of these individuals did (cf. 5:5, 8, 11, etc.). Fourth, the reference to having “sons and daughters” (5:4) does not fit the clan theory.’

6. It has been suggested that a different numerical system (e.g. sexagesimal rather than decimal) is used here.  This was the case with the Sumerian King List, which lists the kings of the pre-flood and post-flood periods.

7. Barnouin theorises that the ages relate to various astronomical periods.

8. For some, the long life spans reflect theological (and not necessarily historical) truth: not only procreation, but long life, is seen as a blessing and hope from God.  Mathews writes:

‘In the Mosaic law long life was the product of God’s blessing for obedience. This was etched in the mind of the community by the Fifth Commandment (Exod 20:12; Deut 5:16), which is distinctive as the first of the commands with a promise (Eph 6:2–3). Long life was commonly tied to the heritage of living in the land (e.g., Deut 4:25; 30:20). Outstanding heroes, such as Abraham, Gideon, and David, were said to have lived to a “good old age” (Gen 25:8; Judg 8:32; 1 Chr 29:28). Strikingly, apart from the patriarchs of Genesis, in the Old Testament only Job (140), Moses (120), Joshua (110), and Jehoiada (130) lived longer than a century of years. Isaiah also points to long life as a feature of blessing in the eschatological age (Isa 65:20).’

McClatchie notes that the Sumerian King List records some absurdly long reigns (thousands of years) for some of the pre-flood kings.  Both, however, are supposed to record kings who actually lived and reigned, even if the lengths of reign are implausible.  Kitchen suggests that the numbers may have been inflated using sexagesimal multipliers.  A reign of 60,000 years (given for Alalgar and Dumuzi), when divided by 10 × 60, would yield a reign of 60 years.  This method, according to Kitchen, works smoothly for all the pre-flood kings.  In the case of the (less heroic) post-flood Sumerian kings, plausible numbers can generally be obtained by appplying a factor of 60 (not 60 x 10).

In Ancient Orient and Old Testament, Kenneth Kitchen advanced the view that the apparent longevity of these individuals does not affect our view of their essential historicity.  Kitchen cites the case of Enmebaragisi, king of Kish, of whom the Sumerian King List states that he reigned for 900 years (Kitchen says 100, but see this):

‘but the stubborn fact remains that this king was real enough to leave behind him early Sumerian inscriptions, so he himself must be counted as historical, regardless of how one accounts for the Sumerian King List figure.’

Turning to Gen 5, McClatchie notes that of the 30 numbers listed, 21 are divisible by 5.  Of the remaining 9, 8 are divisible by 5 5 after subtracting 7.  (The one exception is Methuselah, who died at 969).  Lloyd Bailey observes a similar pattern in the Sumerian King Lists.  In Gen 5, the final digit is 0, 2, 5 or 7 in all but one case.  The probability of ranson ages falling into the pattern is surpassingly small. Compare the random distribution of the length of reigns of the kings of Israel and Judah, as recorded in the books of King – 17, 3, 41, 2, 24, 2, 7 days, 12, 22, 25, 2, 8, 1, 28, 40, 17, 16, 29, 52, 41, 6 months, 1 month, 10, 2, 20, 16, 16, 9, 29, 55, 2, 21, 3 months, 11, 3 months, and 11.

Another similarity between the Sumerian and the biblical lists is that the importance of the seventh person in the list is stressed.

McClatchie concludes that some kind of symbolism is going on in the Genesis account, even if we cannot be sure what that symbolism is.

What About Genesis 6:3? (asks McClatchie).  This seems to teach that from that time onwards a man’s lifespan would be limited to 120 years, which itself would imply that it had hitherto been longer than this.  But this is not decisive, because even after this point some individuals (including Abraham) lived longer than 120 years.  In fact, this verse may not be referring to human life span at all, but, rather, giving a countdown to the flood.

R.K. Harrison (JETS 37/2) discusses a number of possible factors.  He notes, for example, that in some ancient cultures, the measurement of age is more a sociological, than a biological matter.  It is reported, Harrison writes, that ancient Chinese society:

‘deemed a baby to be one year old on the day it was born. Some months later the baby was accorded its second birthday, and by the time that it was biologically about seven years of age by occidental reckoning it could be regarded locally as being fourteen or fifteen years old.’

Moreover, writes Harrison, the ancient biblical scribes may have been following the custom (attested in Egypt and elsewhere) of ascribing great age to a person on account of the contribution that individual was deemed to have made to society.  In some cultures, such a person was deemed worthy of ancestor worship, and the attribution of great age would have enhanced the esteem in which he was held.

See also this discussion.