Hiring girls is difficult (because very few work in the space)

What's the acceptable female analogue of "Guys"? Is there one?

I agree that infantilizing language shouldn't be used, but the company wasn't looking for "Girls" and filtering out "Men", it was looking for "Girls" and filtering out "Guys". So in context, it seems more casual than infantile. The point which really drives this home is actually a comment on the article itself, which slams the author (like you and others here have) for using the dreaded term "girls", and then turns right around and says "Attend Women 2.0 events and check out Girls Who Code", with no hint of ironic awareness.

Words convey a lot, but so does context and tone. Unless you can point to something specific in the article which infantilizes women and indicates that "girls" is being used in the child sense and not the casual sense, I think your ire could be better pointed somewhere else.

I believe it's only illegal to say, "only girls need apply". But, there are even exceptions to that. For example, if you're hiring an TSA agent who's job it is to pat down females, the person you hire would need to be a female as it's a requirement of the job.