Details have appeared on the Arriva Trains Wales site that they are yet again repeating their Club 55 travel offer this Autumn - ie travelling out from 1/9/16 to 27/10/16 (return up to 8 days later).
Essentially anyone aged 55 or over can buy a "Club 55 ticket", a special off-peak return ticket, which entitles you to travel from Station A to Station B and back for £24 (or £29 if you wish to travel on a Friday).
You must travel out on the date shown on ticket and return within 8 days (ie day out + 7). So latest journey is out 27/10 and back 3/11.
Can be bought online or at stations. I'll add more details in the first post below with links.