I used to create Telehealth applications which used Android devices that would just boot into our application and let the user do nothing else. I think our oldest customer was 105, most were over 70. These were used by some NHS PCTs / CCGs.
We actively avoided scrolling wherever possible (in fact I cannot think of a screen that had actual scrolling) as we found it confused users. They didn't even really like pressing the buttons as they were afraid of breaking the devices so would touch it very quickly. Scrolling would have been really out of their comfort zone.
What they did understand was buttons with arrows and text being explicit about what they do. For example we were taking questionnaires about their health, so the buttons would be big and bold, as would the text. At the bottom were two large buttons with "<- BACK" and "NEXT ->". This worked best for us. It would highlight as soon as it could detect touch.
Cannot find any larger images online, but this is the UI in a questionnaire.
Also as you're doing this on mobile, keep in mind that some elderly people do have trouble keeping their hands steady. Any complex (even dragging to scroll) is too much for them.
My best advice would be to keep everything as simple as possible, don't even worry about making it look nice. Our application in terms of style looked horrible but they liked it because it worked and was clear.