IS it inappropriate to show off my knees when I’m rapidly approaching my sixties? Am I too old to wear mini skirts that bare this much leg? These are the questions that rattle around my head when I’m unboxing my deliveries after a late-night shopping haul. I’m a great believer in wearing what you damn well please, but equally I’m plagued by the dreaded “mutton-dressed-as-lamb” self-doubts. My mum wouldn’t have…