I believe this qualifies, more or less, as a computer,
and is
definitely over 10 years old:
http://www.bioeddie.co.uk/models/psion-ll-organiser-lz.htm
I have the main unit, which I've tested and appears to work fine, a
number of ROM and RAM carts, and a bunch of books.
Asking $50, including shipping in the Lower 48. International pays
for shipping (sorry.)