It was commonly taught in typing classes through the late 1990s (at least). I do it myself and am a bit younger than the age range you mention. A likelier cri

It was commonly taught in typing classes through the late 1990s (at least). I do it myself and am a bit younger than the age range you mention. A likelier criterion is whether someone took a formal typing class or worked in a profession related to typing before the advent of WYSIWYG word processors. The justification (no pun intended) for the double space after period is that it looks better, or closer to traditional typesetting, when text is rendered in a monospaced font. While this is still my experience with reading and writing e-mail (and other text) in a terminal, it's not the way most people now compose text on most devices, since most typing is done in software with proportional fonts.