I've just done a small and quick straw poll and everyone knew that sense of 'august' 🤷 I'd agree that it's not used in everyday speech but it's not that rare to read it.

The word "august" used to mean respected/impressive. I am a native speaker of English, living in Canada. I am a senior and have never heard it used as such in any conversation.

Apparently yes, august means impressive/respected etc, according to Google. But I would say 99% of native speakers don't know this, so I would advise against using such terminology unless your goal is to be misunderstood. Generally, personal style can't change universally solid definitions, but context can. For example, legal and academic contexts. These folks love to use words that mean one thing in Plain English, while saying it means something else, just because they say so. They've obviously entitled to dictate their own conventions within the confines of their own organisational jurisdictions though.