I've had people call me "sir" and I'm a woman who looks female (I'm pretty sure anyway), so I'm generally nonchalant about people applying m'am or similar to me. Though I'm from the north and m'am is not very common. I more often get called Miss. My spouse sometimes calls me madam if he's feeling jovial.

I get referred to as a kid all the time, especially at university, and I'm nearly 30. It's annoying but I tend to take it as I still look young so it can't be all that bad...