Use of possessive in "seven years' experience" [closed]

Common usage would be years' when talking about more than one year in a possessive sense. Seven years' means it belongs to a group of more than one year.

I am a super hero with seven years' experience in blowing out fires with my exhalation.

Compare with:

It had been years since I last blew out fires with my exhalation.

For reference: Purdue OWL- Plural Possessive center

To avoid using the apostrophe, you can write

I am a super hero with seven years of experience in blowing out fires with my exhalation.

However using the apostrophe and writing

I am a super hero with seven years' experience in blowing out fires with my exhalation

is fine, because it need not mean literal possession. Here the apostrophe simply means that the experience is related to the seven years in some way, much like in men's shoes or doctor's appointment.