I disagree with the people who say that the worker can't catch a break - just don't ask! Management should just post a sign offering a Senior Discount, and what age they consider "Senior". Believe me, if people want the discount, they'll ask.
I worked at a theater for 4 years. There was a sign for senior discount clearly posted right where you buy your tickets. Multiple times a day we would get complaints from seniors who did not get the senior rate because they did not ask for it. If employees asked, people get mad. If they don't ask even though it is clearly posted and hard to miss, people get mad because they didn't get the rate.
People are way too sensitive about their age. The employee is just trying to save you money.