Maybe not. Anti-discrimination laws are allowed by the constitution. Those laws can prohibit certain speech. That's well established and tested in court.
You are absolutely correct that the law can prohibit certain speech. Yet there are only three categories of speech that can be prohibited. 1. Obscenity 2. Fighting words and 3. Threats or incitement to violence. Let's see if this fits within any of them:
1. Reporting age is not obscene. Miller v. California (1973) requires that:
*The average person, applying "contemporary community standards", would find that the work, taken as a whole, appeals to the prurient interest;
*The work depicts or describes, in a patently offensive way, "sexual conduct or excretory functions" specifically defined by applicable state law; and
*Whether the work, taken as a whole, lacks serious literary, artistic, political, or scientific value.
The average person does not believe that discussions of age are prurient. Nor does reporting age involve sexual conduct or an excretory function. Finally, reporting age is of serious "scientific" value -- we do everything from condition certain privileges and benefits based upon age to discuss accomplishment with respect to age. Even if you dispute the latter point, it's an "and" test, so you would have to satisfy the other factors as well.
2. Reporting age is not fighting words. Cohen v. California (1971) and Snyder v. Phelps (2011) limit that doctrine.
*Cohen held that wearing a jacket that said "fuck the draft" was outside the doctrine because it was not a "personally abusive epithet";
*Snyder held that the Westboro Babptist Church's funeral protests were outside the doctrine because the speech was was not personal but instead public; and
*Most courts also require physical proximity between the speaker and the target -- and there's no such proximity here.
You're not going to get a jury to unanimously hold that reporting someone's numerical age is a personally abusive epithet. Reporting an age is also speech that is public rather than personal -- it is not made at or to the person, but the public at large. Finally, there's no proximity between IMDB and the person that could permit an immediate breach of the peace, i.e., a physical altercation.
3. Finally, reporting on age does not constitute a threat, whether personal or general. Brandenburg v. Ohio (1969) requires that:
* the speaker intend to incite a violation of the law; and
* that the violation is both imminent and likely.
You're not going to get a jury to unanimously hold that reporting someone's numerical age is intended to create age discrimination. Also, there's no imminent, i.e., immediate, connection between reporting the age and any individual incident of age discrimination, nor is any such discrimination likely as opposed to merely being "possible."
So the issue here is if publishing actor's ages against their wishes is possibly discriminatory.
No it's not. The issue here is whether the reporting fits within any exception to the first amendment. It does not.
You could have figured this out without much familiarity with the law. Publishing information itself is not "possibly discriminatory" -- it neither conditions nor denies a privilege or benefit based upon the person's age. You're arguing that someone else might use that information to discriminate -- but that's an entirely different and separate kettle of fish.