I'd say the guy has a good case here. Oregon law does include age discrimination in public accommodation laws (as long as over 18). The only exceptions are for things that are already age limited higher in laws, like alcohol and marijuana.
Civil Rights Division ENFORCING CIVIL RIGHTS LAWS
"A place of public accommodation is defined in state law as any place that offers the public accommodations, advantages, facilities or privileges, whether in the nature of goods, services, lodging, amusements or otherwise. It is illegal to discriminate in places of public accommodation on the basis of race, sex (including pregnancy), sexual orientation, national origin, religion, marital status, physical or mental disability, or age (18 years of age and older)."
Personally, I think people need to just be legally an adult at one single age (prefer 18 since that is when most people graduate high school and get out on their own, making their own decisions). I'm for changing alcohol laws (and marijuana laws if they are at alcohol age rather than cigarette age) to 18. And I'm against not renting to those under 25. In fact, over 20 years ago car rental places in at least NY were told that they had to rent to those under 25.
https://www.nytimes.com/1994/11/30/nyregion/car-rental-companies-ordered-to-accept-young-drivers.html
https://ag.ny.gov/consumer-frauds/car-rental-tip-sheet
It will depend on if a state includes age in their public accommodation laws, but at least some do. And part of it comes down to things like whether anyone has challenged policies or not as well.