I believe SCB has answered correctly. There are zones with different prices, but a zone only has one price; regardless of where it is or the demographics of it. It may be unlikely - maybe not the way they are treated - but what if no oldies or kids choose to go in Z1, would al of those supporters in there be receiving a concession, or just the going tariff for that zone?
I have used the term 'a broad reasonable interpretation' throughout, it is more commonly used in patent adjudication. It can also be applied when folk want to dance around what a word, such as concession, really implies. Reasonable can be a compelling argument.