Well i have old man over 70 years and he mostly understable a W7 new version are complicated for him. He saw how many often times I using a Linux and he want trying a some not difficult Linux Distribution.
Simple with not to much complicated. Propably mint is more simple from Zorin.
Have you got more ideas what help him not difficult linux distribution.
He tried Zorin but maybe something more simple without many software and etc.
Propably xfce will be best option - old people don't liked when have something and not working for them this is annoying because they are confuse and mostly don't understand what is going on.