There may be some terminology confusion.
To your question, 241 is better than any on the door age-discounts, Bletchley Park youve mentioned will be much better with 241/days out than the concession rate.
Discounted entrance at the door is called a concession rate, (different meaning to in-store concession) the term Senior isn't really used here as its too ambiguous, we used to see Senior Citizen or OAP but these are not used now.
(concession rate can include any group or persons in the attractions list) there is no definite template, you need to check, attractions make their own decision, 60+ ( and younger adults is quite usual) but at HCP its 65+.
And at the Postal Museum and railway 16-24 has the reduced adult rate, nothing for 60+.
The discounted (concession) rate to attractions isn't significant, perhaps £2 or £4,
241/days out is a railway company promotion, to encourage train travel during quieter off peak times, it's aimed at residents who live outside the area where the attraction is, they go to their local station, buy train tickets each and bring the 241 voucher booklet and present these at the entrance.
There is a 12 month two-together Railcard (@ 1x £30)two named holders use this, but not financially viable on short visits unless you are making several long distance train journeys.
There is a 12 month 60+ Senior Railcard, @£30 per person, again needs to be financially worthwhile to recover the outlay.