I don’t think Abraham’s age is a mistake. The lifetimes of humans gradually decreased after the flood. We are currently genetically limited to 120 years. The oldest “modern” person (Jeanne Calment (1875–1997) of France) has been recorded to live to 122 and there is even debate about that.
For example:
Noah lived 950 years
Shem lived 600 years
Arpachshad lived 438 years
Shelah lived 403 years
Eber lived 464 years
Peleg lived 239 years
Reu lived 239 years
Serug lived 230 years
Terah lived 205 years
Nahor Abraham’s brother lived 148 years
Abraham lived 175 years
Sarah lived 127 years
Isaac lived 180 years
Jacob lived 147 years
Joseph lived 110 years
Moses lived 120 years
Joshua lived 110 years
David lived 70 years (it doesn’t actually say 70 but David was 30 when he became king and he reigned for 40 years)
David and after it never actually says how long they lived. It says how long a king reigned and sometimes how old he was when he began his reign so you could extrapolate from that but they were all under 120 years old.

Here is the YY translation of Bare'syth 6:3
Bare'syth 6:3
Then (wa) Yahowah said (‘amar – communicated using words (qal imperfect)), ‘My Spirit (Ruwach ‘any – Spirit of Mine, always feminine in the text; from ruwach – to accept as a result of being perceptive, to facilitate understanding, and to provide relief and restoration, enlarging an individual and expanding their capabilities over an interval of space and time) shall not remain nor abide (lo’ duwn – will not dwell nor contend with, will not plead with or vindicate (qal imperfect)) with the descendants of ‘Adam (ba ha ‘adam – with mankind, humans with a neshamah – conscience) forever (la ‘owlam – indefinitely or eternally, for an unending duration of time) because (sha – for the reason and to make a contrast) additionally (gam – besides moreover and in addition), he is (huw’) flesh and prone to preaching (basar – biological life, an animal, a corporeal construct subject to decay; based upon the verbal root, basar – to proclaim, publish, and preach news considered good and beneficial by those who hear it). So for a period of time, it shall exist that his days will be (wa hayah yowmym huw’ – therefore it shall actually and for a limited period, that his time shall be (qal perfect)) one-hundred-twenty (me’ah wa ‘esrym – a hundred and twenty) years (shanah – repetitions of the seasons, times to change and be different, repeat of the solar year).

It's been my understanding that this doesn't mean age of a human being before he dies but how long he will contend with mankind. 120 Jubilee/Yowbel years is 6000 years which if accurate isn't much more time to contend.