The "Senior Discount" is not a law. It's a voluntary accomodation that merchants give to people who are 65 years and older. The reason this happened at all was that merchants finally realized that older Americans were on "fixed incomes", and that they were losing a vast segment of society due to higher prices. So, they concluded, that making a smaller sale, or profit, was better than making no sale at all - - thus, the "Senior Discount" was born.
A 35 year old is not necessarily on a fixed income, and their "earning capacity" - - when all things are equal - - are far better able to afford the "standard" prices than are Seniors.
So, don't rock the boat. Remember, it's voluntary - - and merchants don't have to offer any kind of discounts, to anyone, if they don't want to.