True love waits

3 When Adam had lived 130 years, he fathered a son in his own likeness, after his image, and named him Seth...25 When Methuselah had lived 187 years, he fathered Lamech...28 When Lamech had lived 182 years, he fathered a son...32 After Noah was 500 years old, Noah fathered Shem, Ham, and Japheth (Gen 5:3,25,28,32).

1. Commentators puzzle over the longevity of the antediluvians. There've been some ingenious efforts to decode the ages as symbolic, but I haven't seen any consistent numerological principle.

2. There's nothing especially surprising about the longevity of the antediluvians. From the standpoint of biblical anthropology, man originally had the capacity for biological immortality. That opportunity was lost when Adam and Eve were put out of reach of the tree of life, but in the world to come, the redeemed will regain what was lost in Adam.

3. A more puzzling, but neglected feature of the genealogies, is the age at which the antediluvians fathered kids. Was Adam a virgin until he reached 130? Was Lamech a virgin until 182? Was Methuselah a virgin until 187? Was Noah a virgin until 500 years of age? That would certainly make the antediluvians impressive, if discouraging, role-models for abstinence-only programs. Lends exponentially new meaning to "True love waits!"

On the face of it, there are two possible explanations:

i) The reason the antediluvians lived so long is because their lifecycle was slower. They took much longer to reach sexual maturity. Slower means longer. Like the difference between human years and dog years. Or to put it in reverse, the lifespan of postdiluvians is accelerated.  

ii) The other, perhaps more reasonable explanation, is that Gen 5 isn't recording the age at which they first fathered a son. Rather, the genealogies are selective. The purpose is to sample some representative descendants to establish a lineage. List enough descendants to trace a starting-point and end-point. 

If the age at which the genealogies record the birth of a son has that function or significance, then it's evidence that the genealogies are open rather than closed. If so, that has some bearing on using the genealogies to reconstruct an absolute chronology.