Technically this is discrimination based on age.

They were born 4/20/(year). You could make an argument they are discriminating all people exactly (X) years, 4 months, and 2 days old.

Age discrimination only applies if you're above 40.

Creative thoughts, but the exact definitions don't track (from GINA):

Genetic information.--

(A) In general.--The term "genetic information" means, with respect to any individual, information about--

(i) such individual's genetic tests,

(ii) the genetic tests of family members of such individual, and

(iii) the manifestation of a disease or disorder in family members of such individual.

(B) Inclusion of genetic services and participation in genetic research.--Such term includes, with respect to any individual, any request for, or receipt of, genetic services, or participation in clinical research which includes genetic services, by such individual or any family member of such individual.

(C) Exclusions.--The term "genetic information" shall not include information about the sex or age of any individual.

I doubt it - your age isn't determined by your genetics. The family medical history part is so that someone doesn't fire you (or not hire you) for things like your mom having a kind of cancer that is hereditary. As a manager, if one of my employees tells me their mom has cancer, I'm not allowed to ask what kind.

I believe it's legal in the US to pass someone over for promotion because they're too young. The only protected class related to age is being over 40 (potentially different in some states).

but now that I think about it, this is only really a protection if you’re already hired at the place. If you just slam the door on people before they can get in, discrimination seems to be legal.

Pretty sure that protection so applies to the application process. Can't have places rejecting every non-white candidate for being the wrong race. The problem is proving that you were rejected for a BS reason is really hard because they usually don't flat out say it, and especially not in writing

Being denied a promotion because you're "too young" is certainly a protection.

It's not actually. Age protections really do only apply to old people. If the person in the post is over 40 though, and got rejected for their birthday, they could probably at least get the company to overturn the rejection. Not sure how well they'd do in court. Most of this stuff doesn't get enforced well, and that one is already a stretch

They listed the protected classes. Which one is astrology?