In a previous post I mentioned that a laptop may not be the best choice for an older user because they may need a large screen because of vision problems and a separate keyboard because of mobility issues. To expand on that theme, here are two more reasons that a desktop setup may be the better choice.
1) Many older people have an awful time trying to move the cursor around the screen with the touchpad that is typical on a laptop. Using a mouse is difficult enough. The touchpad is nearly impossible for anyone with hand tremors or severe arthritis.
2) Laptops are by nature portable. But an older person with unsteady gate or coordination problems may not appreciate that portability. What you see as an advantage they see as a hazard, something that they can drop and smash.
And while I'm on the subject of mobility issues, when shopping for a computer for an older person be sure to take a look at some of the all-in-one models like a Dell Inspiron One or an Apple iMac. They will be much easier for a senior to manage simply because they'll never have to get down under the desk to turn the damn thing on or off.