When my mother moved into an assisted-living facility a few years ago and was thinking about buying a new computer I tried to talk her into getting a laptop. She bought a desktop instead and I was a little miffed that she ignored my advice. I was wrong.
She made exactly the right choice, and here's why it might be the best choice for you or someone you know:
The two things that she really needed the most in a computer were a really large screen and a full-size keyboard that she could move into a position that was comfortable for her. Neither of which is available on a laptop.
And the one thing that I thought she would appreciated about a laptop, the ability to carry it around the facility, downstairs into the sitting room or outside onto her patio, was the one thing she had zero interest in.
The issue with the screen is key. A lot of older people have problems with their vision and have their browser settings adjusted to zoom in so that they can easily read the text. But then, when they're looking at a website they can't see a whole page on the screen at one time.
Which, besides being really annoying, turns out to be compounded by other common difficulties, decreasing eye-hand coordination and/or tremors.
Imagine how frustrating it must be when the only way to see the whole page is to scroll up and down and side to side and you're having trouble getting the mouse to go where you want it it.
So now I recommend a desktop for most older users if they have the space for one. Or at least an external monitor connected to an existing laptop. Get them the biggest screen that's practical.