This was mentioned a couple of times here. Seems 2 spaces at the end of a sentence indicated “old foggy” to them. Here is a view that they are wrong. So take that you millenials.
For anyone who learned their keyboarding skills on a typewriter rather than a computer—and for the many who developed their keyboard muscle memory using software packages such as Mavis Beacon Teaches Typing—the double-space after the period is a deeply ingrained truth. While modern style, based on the fallacy that computer typography makes such double-spaces redundant and Paleolithic, has demanded the deprecation of the second tap of the space bar after a punctuation full-stop, many have openly resisted this heresy, believing that the extra space is a courtesy to the reader and enhances the legibility of the text.