Use your brain, old man
I’m the HR person where I work and I must say, I am completely appalled at the number of people who apply for a job with a cover letter that begins “Dear Gentlemen” or “Dear Sirs.”
I mean seriously. We’re a good 40 years beyond that, aren’t we? Basic common sense people. If you’re so ignorant that you think only men would be in a position to be reading your resume OR you think that Gentleman is still an appropriate default professional greeting, then there is really no place for you in the technology industry.
The greeting you chose for your letter tells me that your tech skills are very likely to be wildly outdated and your cross-gender communication in the office will be really awful. Your unwillingness to either accept that a woman might be in a position of authority over you or to adapt to changing times makes you unfit for this business. Any business, really.
Just retire, buddy. You’re done. Go buy a house on the river and a Winnebago and enjoy the time off.