That's accurate for federal law, but I think a log of states are more strict. At least New York is:

> The New York State Human Rights Law covers employers with four or more employees. It protects persons 18 and over from age discrimination in employment

> An employer may not refuse to hire or promote an employee, and may not terminate an individual because of age, and must provide the same terms and conditions of employment irrespective of age, including salary.

https://dhr.ny.gov/sites/default/files/pdf/age-discriminatio...

That goes back to my original example. If I can’t “discriminate” against an 18 year old, does that mean I can’t require someone to have a BS degree in Computer Science and 10+ years of experience?

No, I'm pretty sure the restriction here isn't based on a "disproportionate impact" judgement, but on intent. As long as you have a reason to claim you applied the college degree qualification, you're fine. The minute that a court subpoenas your emails and finds that you added the restriction with the explicit intent of preventing young people from getting the job, you are in for a world of legal hurt.

This is exactly how it works for most other hiring discrimination too. If a court finds an email titled "how we can use a college degree requirement to decrease the number of Hispanics at our company" you have a problem, but requiring a degree isn't itself illegal even though different races currently graduate from college at different rates in this country.