theres only 3 answers here
#1 fiction
#2 interpretation error
#3 man lived to 900+ years
we know man doesnt and has never lived past the average 120
so is it #1 or #2
We know there have been people who lived past 120 years old. This has been documented and was even posted earlier in this thread. I worked in the longevity field and simple things like caloric restriction with optimal nutrition(cron) from an early age can give a person double the normal lifespan. So now we are at about 160 years old. There are epigenetic studies which show your grandparents diet can increase or decrease your lifespan. So its possible that several generations of caloric restriction could increase lifespan even further than 160 years. We know from studies with animals such as worms that some manipulations can increase average lifespans of the worms 6 times. Apply that to humans and you are now at 400+ years old.
I can go on but im not sure you will listen. To say people dont and has never lived past 120 years old or that its medically impossible or men cant father children at that age, seems to deny what the research in animals has shown.
Clearly not everyone will live this long even in the conditions shown in animals but it has already been pointed out that you are only talking about a relatively few people in genesis. We dont know for sure that these same conditions applied to humans will have the same effects but it doesnt seem logical to say its impossible or that it can only be fiction.
There are other possibilities of mistranslation or misinterpretation etc. for genesis. But i dont see how you can rule out a person living to be 200 years old, considering what the research in animals has shown.