That has been speculated, but it then means some of those people are giving birth at age 6, which is why it is not universally accepted as an explanation. There is another version of the text that adds another 100 years to age-of-fatherhood, which makes this explanation more plausible if the extra 100 year variant is the correct one, but there are still some ages which are way too young if measured in months and way too old if measured in years.

That theory would assume the men from Adam to Noah are actually historical persons with recorded timespans, and there was just some mistake in interpreting the numbers. But consider that Noah is similar to a character known from much older Sumerian flood myths - except in the Sumerian version he is immortal. It is common to ascribe impossibly long lifespans to legendary figures from past ages - the Sumerian list of kings lists their early kings as having reign of tens of thousands of years.

I think it is a fools errand to try to find rational explanations for implausibilities in mythology. After all, the length of lifespan is kind of the least problematic thing about the account of Adam, if you want to understand it as historical.