In my experience the biggest problem for elderly people is was is shown on the screen. I see some inactive windows, one active with scroll bars, a menu line and probably a tool bar with icons below and finally a status information in the bottom part of the window. My mother (68, seven years of light computer experience with XP) only sees a complete mess. A heavily simplified desktop would be nice.
It's fairly simple to do even in a standard Linux. Look at this screenshot:
This is an overly simplified situation with just two possible: Power off or run "the internet". You could easily add a mail application and so on. And it's easy to make the icons bigger.
The point is that this desktop is done by just using a low-end WM (BlackBox/OpenBox), an iconmanager (xtdesk/idesk) and a little bash script to integrate these elements. All together it's much less than 1 MB.
(Thinstation is a x86-only thin client and useless by itself for Raspi - but inspiration is free)