And created a new page for it on NRE:
https://www.nationalrail.co.uk/ticket-types/tickets/nfp/
Not that most people will read that when buying a ticket, of course. They'll just see a ticket at a price they're willing to pay and buy it.
In the app, if you choose "show details" for the ticket, it gives the restriction code as AC (with link) and gives a link to the "NFP" page as "additional information". So not particularly obvious to me that the additional information is actually additional restrictions. (Though I appreciate that the restriction code probably isn't the right place for an age restriction).
Personally I think they could have done better.
(Especially as on my phone, the pages linked to don't actually show).
One doesn't normally have to go digging around in additional information to find out that having asked for an adult ticket with no discounts, that's not what you're being offered.
It reminds me of the when is an anytime ticket not an anytime issue with railcards.
The
restriction code is that of a regular advance with no mention of age restriction but even though it has "advance" in the name it's actually a different
ticket type so one must look up the rules for that ticket type.
It also seems a bit mean to offer 50% off advance fares for those over 60 and no advance fares at all for anyone else.