Yes, you can ride both of these scenic train rides as senior citizens. My husband and I are both senior citizens and we just recently did both of these train rides as well as the Bernina Express. One way you could do both train rides is to take the train from Basel to Lausanne and ride the Golden Pass to Interlaken and continue on to Murren. Once you leave Murren you could start on the Glacier Express at Visp and ride it all the way to St Moritz as this would also provide you an opportunity to ride part of the same line as the Bernina Express. If you do not want to travel all the way to St Moritz you could end this ride at an earlier city and then go to Luzern. That is just one plan, there are various ways depending on what cities you wish to visit and the number of days in each city.
We just returned from Switzerland and connected three of the scenic train rides into our trip. Arriving in Zurich we took the train to Chur and rode the Bernina express almost into Italy. We then took a regular train back to Chur and spent the night. We had ridden the Bernina express on our last trip five years ago and like it so much we decided to do it again. Really enjoyed it and did not regret repeating it at all.
The next day we went from Chur to Zermatt on the Glacier Express. We had never been on the Glacier Express or to Zermatt and really enjoyed both the train ride and visiting Zermatt and the Matterhorn. After a few days in Zermatt we went to Murren for several days. Then we rode the Golden Pass from Interlaken to Lausanne, again a train ride and town we had never visited. From Lausanne we went to Luzern, spent a few days and flew home from Zurich.
We found we really liked the Glacier Express and Bernina Express. The Golden Pass provided different scenery to a region of Switzerland we had not visited before but was not as scenic or interesting as the Bernina or Glacier train rides. But we were glad to have visited additional areas of Switzerland different from our previous trip.