Haha. I was called Ma'am a few months ago. By a boy who works in McDonald's. I was outraged.
I'm only 25!
Maybe it's part of McD customer service training? I was also called madam by a young lad last time I went through a McD drive through. I got asked for ID trying to buy filter tips in Waitrose the same week though so in my mind the two have cancelled each other out and I'm in some magic space between young and old (or possibly deluded... aged 33)