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.