If you want rural, there's Craibstone - easy access to AWPR.
I personally would consider Westhill - great for older folk as you can walk to everything - doctor, dentist, food shops including M&S, Tesco, Aldi, restaurants, and buses into town. It's also close to woods and walks. (I plan to move there myself when I get too old to drive). An easy drive to hospital if it's not rush hour.
Avoid up the hill in Elrick as the developer seems to be changing the maintenance management company often and every time the fees go up. You will be paying for the three playgrounds that you will never use, and roadside grass cutting.
Not Kingswells. It has a microclimate so roads get icy in winter, but the gritters never think the area is a priority.
The newest Cala development in Cults is very nice and a couple of houses are up for resale. Mannofield, Bieldside, Peterculter and Hazlehead area are all worth considering.
Fifeshill Drive in Countesswells, but not the new development with social housing in a different part of Countesswells. As another poster said, there are a few problems developing. The last time I went to the Sainsbury's there, school kids were loitering at the entrance, pestering shoppers to 'buy me something!' A gang of kids can be intimidating to older folk.
I wouldn't live in Dyce, and Stonehaven/Banchory/Inverurie are too far from ARI for you.
HTH