In my lifetime, there was a new term invented to address a grown female (any age). It's Ms. (pronounced mzz). It isn't short for anything, it was devised because there is no need to know if a grown female is single (Miss) or married (Mrs.) in order to address her formally.
I'm a 78 year old female, and if someone in this day and age addressed me as "madam" (or "ma'am"), I would probably be startled. It's not offensive, just surprising and old fashioned. So whatever the age of an adult female, you can safely address her as Ms.