The ages of the patriarchs are almost certainly some sort of Hebraic numerology that has been lost to history and may have been influenced by different traditions (the ages in the Septuagint differ, for example). After all, the fact the majority of them are divisible by 5 is an interesting data point (compared to the lengths of rulership of kings, much later, which appear randomly distributed).

Lloyd Bailey wrote an interesting (non-peer reviewed) paper on the subject, "Biblical Math as Heilsgeschichte?"[1] and Ben Stanhope in "(Mis)Interpreting Genesis"[2] covers it as well.

[1] https://drmsh.com/wp-content/uploads/2015/12/Bailey-Biblical...

[2] https://www.amazon.com/Mis-interpreting-Genesis-Creation-Mis...