His implication is that the only reason an eighteen year old girl who is attractive would be offered an internship is that she is an attractive woman. You're not even questioning it. The way the author wrote it is messed up.
hmmmm, can I get through your own sexist brain? (Not an ad hominem, I just feel you're also being sexist.) Let's try this, this may or may not work. Close your eyes and imagine that you've studied very, very hard throughout high school and through very hard work you were admitted to MIT. You're also an attractive woman, which is irrelevant. You're reading HN, and then the linked article. Now how do you feel reading that blog post and its implication?
>married hetero male founders: we're thinking of getting an intern
>me: okay but I don't see what we could offer you know we're on a really tight
>married hetero male founders: we're getting an intern.
>intern: (beautiful 18yo girl)
did I get through to you?