It's great to hear that you have plans to come over and visit us next summer, it looks like a wonderful itinerary for your 3 weeks!
The travel pass scheme for over 66's was for just that one year and hasn't been renewed, unfortunately. If you plan to travel by rail to some of these locations, then Irish Rail
does have some tourist tickets for 4/5 days that may be of interest to you. If not, then booking online more than 7 days in advance also gives a sizeable discount on fares. There is also some information on accessibility
which you may wish to look at too.
For more information on what travel options there are, Transport for Ireland
has a very helpful travel planner where you can search for the most suitable option whether train or bus to get you from location to location.
We hope this helps and that you enjoy your time with us next year!