That is brilliant!
I think it is someone under the age of 30. I'm 36 and I learned to type on a typewriter and everyone I know went off to college with one. There were a few computers in use at the time which would be similar to today, but almost everyone would have been familiar with an electric typewriter.
I think about 5 or 6 years after me would be a pretty good guess for someone to not be familiar with a typewriter.