Purr purr, the Bible is just a collection of folk tales which has been used to beat religious people over the head with.
How do we know how old a person was at death?
The wear on the teeth from the time when a lot of gritty matter was chewed is a good immediate reckoner for death age. Teeth could be completely worn down to the gums by forty years old back in the Bronze Age. Also taking note of the sort of life they led such as highly developed muscle attachment points on the bones indicating heavy manual labour or in the absence of such development, it would tell of a passive and possibly elite lifestyle. Joint wear indicating arthritis was commonly found but not on the very young but universal in the aged. So taking this background information firstly then for the forensic archaeologist, the skull becomes the focus.
As we age, right from birth our skull which is made up of five bony plates, is constantly closing up and smoothing over until about fifty years old. (It never fully fuses). A new born has the fontanelle pulsing on the top of its head which closes within eighteen months but the fine meandering fissures joining the plates of the skull, called sutures, seal up at a recognized rate giving the age of death. For example the saggital suture along the top of the skull behind the fontanelle will usually close up at 29 years old in a healthy person.
In the cemetries of Egypt in the Greek controlled city of Alexandria in the third century CE, there have come painted portraits of the deceased, lots of them. I have twice seen an exhibition of these and was greatly struck by the early deaths in each case and these were people who were not peasants and Alexandria was at the time the greatest and most advanced cosmopolitan city in the world. Mid to late twenties was a common age for death with no one older than early forties as I recall.
Hyperbole (pronounced hy Per bo lee) or gross exaggeration, is a literary device in ancient story telling which would account for the absurd ages of the heroes of old.
Don't take the Bible literally!