Designing user interfaces for some hypothetical "average person" that's using it for the first time might make sense for consumer software that's sold to everyone for occasional tasks, but there's plenty of software that benefits heavily from having a bit of a higher learning curve in exchange for faster/more efficient interaction.
I think the main hindrance for most people is not lack of touch typing skills, but more lack of ability or desire to memorize key bindings or the names of commands.
(On later reflection, I have actually thought of three that I know or used to know that can type at a decent speed. But I can think of quite a few more that can’t.)
I work in metal fabrication, and I can tell you the overwhelming majority of building and fabrication tradespeople can’t touch type, regardless of age.