Just get an ipad - I got a cheap second hand ipad 1 for my mum (85) and she picked,up using it just fine. I never have to help her much unlike her normal computer.
To the poster who said about CPU / graphics power, potentially don't worry as most older folk are only really looking to use the web and read email, neither of which are intensive.
To the poster who said about full size vs compact : in my mums case she asked me to get her an ipad mini after playing with mine. In her case it wasn't about the screen size but because her arms aren't too strong it's easier for her to hold up and use! The air might be an option these days but it's a lot more money...
In general I think that like children, you shouldn't "dumb down" stuff for old folk unless you absolutely have to. It's not as necessary as many would have you believe. In children having to think more helps them learn and in older folk it helps stop them forget!