Was there just last week-again.
It differs for DPP=urban metrotrambus OR trains (CD and an odd ARV line,as is in fact also clearly explained on the site of pid=the regional transport ´verbund´.
It was also changed-again recently per 1/4, but site should show current details.
DPP is FREE for anyone from 65 (and half fare from 60-64), but those from 65-69 must first get a pruvoz duchodne (=fotocard)-at any DPP office (EXCept at airport!), bring 1 passport foto and show ID, pay 60 CzK. FROM 70 this card is not needed FOR DPP!!-just show ID-in the very rare cases that there are checks (normal boarding is unchecked-even i night buses). I did not have 1 single ticket check on DPP during my 3 day stay with many trips. This should apply to anyone-the CZ text says: with ID from EU OR passport from others, and as you know your UK refrains from the much easier to take ID-cards.
For TRAINs INside Praha (all stations labelled as such) you must always have that pruvoz-there is also one for 70+. OR you can use the Litacka (=flyer) chipcard, but this needs time to produce for you, as its personalized.
OUTside of the Praha urban area (quite big, includes airport) seniors >65 (ANY) now get just 50% discount-it was for a year or 2 75%-since 1/4-so this means its doubled from very low to low now. Applies to all means of transport-any ID/passp is enough. Ask for senior ticket.
A 24 hr dayticket for Praha is now 120/130 (?) for normal fare, for the whole PID area (=central CZech province) its 300 for adults and just 90 for those >65, as PR is free and the rest 50% off. BUT to ride the trains with it-see above, you also need that fotocard.
BTW-several other CZ cities, but not all, offer more or less same. BRNO also from 70 and Pardubice and Plzen and Olomouc from 65-again only for their own bustram and not the fare-integrated trains. There ID or passp is enough. Other offer very, very cheap yearly seasons for seniors-effectively thus keeping it for their locals.
IF you mean the country wide tickets for trains: these have gone up a lot recently (apparently they needed extra income there) and there are for whole country (ONLY CD) or for any province (depends on how advanced that province is in creating a unified ¨verbund´style faresystem). IF a province (f.e. Usti nad Labem or Plzen) is now fully integrated, CD has stopped selling its own daytickets for trains only. There are also NO discounts on them for seniors, so you do at least to do double the ´normal´ amount of travel to get its worth out.
There are efforts to create a unified all-company fare system, its labelled OneTicket but still in its infancy and I assume also not widely known.
In summer=july+august CD has the last 4-5 yrs always offered a very cheap 1 week / 7 day railpass, only for its very own trains, but in sept this will not work