Not just old people. Hackernews skews technical and seems to mostly interact with other technical people.
There are people in their 30's, 40's and 50's who don't own a computer at all (other than a smartphone), don't interact with computers on a regular basis, and almost exclusively use the built-in talk/text/browser apps that come pre-installed.
It may be a relatively small percentage of the adult population in the US, but it is still many millions of people.