-- snip -- I responded and she continued: “Right, well, it’s because you’re young and female.” -- snip --

I feel like I missed some steps here. It sounds like it went like this: Person agrees to job. Person signs agreement. Person declines job.[1] The male cofounder contacts this person and offers more money, a better position, and reporting to him.

Then we also learn the author had been considering leaving for a while.

So three things in play:

a) candidate was offered a much better deal to come on board[2] and

b) maybe the candidate picked up on her potential lack of commitment, even the fact that in her mind she was not sur about staying with the company. Perhaps he did this on a subconscious level - making this something that would be hard to put his finger on. Comments about her "energy level" seem to hint that this may be true as well; and

c) maybe the candidate had an issue with gender.

A couple of other revealing snips:

"As a co-founder, your role is to attract the best talent to compete in the market" and "The answer is not hiring quotas or prettier bathrooms. It’s strong leadership."

It seems to me that - regardless of gender - it is possible that the author does not or did not at the time possess these qualities. And that is a deal breaker to certain types of potential hires.

There are simply too many variables in this equation to conclusively state - as the author has done - that her gender was the obvious catalyst to his vacillation.[3]

[1] Do you really want to hire someone who breaks his given word so easily?

[2] Actually this means one of two things: he went back on his word to another company, or he never had another job lined up and was just playing them for a better deal. Either way: not someone I'd want at the top of my org .

[3] Alternatively there is information omitted from this account that would make the rationale more clear.

edit I can English.