All Ages. commonly used in naming events, concerts etc. to distinguish between 18+ shows (bar) or events that allow all ages as long as people have I.D to prove their age for alcohol consumption.
person: thank god ____ are playing an A/A show this friday, or i totally would not have been able to go!
To go dutch (i.e. to share equally some expense or cost between two or more person). An uniquely Hong Kong slang prevalent in the 1960s and 1970s, and sometimes still heard today. Comes from the medical term to mean "in equal parts."
Let's go a/a on the 10-dollar meal. That's five from each of us.