I am surprised at how many people thing Ma'am and Sir make you sound old. I was trained by my military parents to always say them. And to never call an adult by their first name. I am 22 and STILL have an issue with calling people older than me by their first name. If they say "call me Susan" as opposed to Mrs. Insertlastnamehere I ask if I can compromise and say Mrs. Susan. Just, it is so ingrained into my mind, it feels disrespectful not doing it.
Sometimes the Ms. and Miss thing can be confusing if you don't know enough about the person to know what to say, Miss should always be default, though, until you know otherwise.