The body language is quite distinctive - tentatively pressing keys with an outstretched index finger as if the keyboard might jump up and bite them, pushing around the mouse with their fingertips rather than grasping it with their whole hand, leaning away from the screen as if it might explode in their face.
Some older people just can't internalise the idea of looking at the screen for clues as to how to proceed. No matter how many times they're told and shown, they just don't get the idea that computing is interactive. They try to memorise every interaction as a series of rote steps, so if something unexpected happens they're completely lost. They are completely incapable of navigating a UI without very explicit instruction, even if it's broadly similar to UIs they know how to navigate. Something as trivial as accidentally scrolling down a few lines on a website is a complete showstopper. I don't understand it, but I find it endlessly fascinating.