Hello Leacheghoi57
Simply go to the train station’s travel office at Zurich Airport to purchase the tickets. The ticket from Zurich Airport to Zurich main station (Zürich HB) will also allow you to use the tramways and buses in Zurich.
With these few trips, a Swiss Half Fare Card hardly makes any sense. But, inform the travel agent on your plans and the person will sell most beneficial tickets.
For the Zürich HB to Geneva, there might be Supersaver tickets available. However, without any information on the date of travel, it is difficult for me to look up fares and to suggest anything; please instruct.
There are no discounts on individual tickets for seniors.
Kind regards,
Roland