The evidence is starting to appear that supports mask use. I do feel sorry for the poor old pensioner in your scenario but surely they’d have a hanky which they could cover their nose and mouth with?
P.S. I do wonder as Grant Shapps said he was aiming for 10% of public transport use a good while ago which is not realistic in the real world whether face coverings is a real world compromise.
Face coverings I think are useful, just I had doubts as those with links to asian countries voicing that it was a definitive solution and some scepticism around Italy where they were very widely worn (but eye coverings were seen as nonsense). Also worries about supplies going.
Still don't know how you get around the use indoors where the government recommends them and no one is using them. The latter policy may help the former.