In my town, senior discounts are strictly illegal.I'm not sure that every state, or even Oregon, interprets its age discrimination provision in public accommodations law as strictly disallowing any differential treatment for anyone over age 18. Do not some bars disallow people younger that 21? And, as you noted, senior citizen discounts at movie theaters and restaurants are, strictly speaking, forms of age discrimination.
But would you want to be the prosecutor who hauls Quality 16
Theaters into court, & deny us old fogies our discount?
Political power often trumps the law.