When is your 60th birthday?

After the 60th birthday, it happened in many places. My hometown is Shanghai, and Shanghainese call it the "birthday celebration" for the elderly. Every ten big birthdays is a big birthday. People ask, "Nine or ten?" They didn't say ten. Why? Coincidentally, the pronunciation of "ten" and "thief" in Shanghai dialect is the same. Who wants to be a thief? In addition, the 60th birthday on May 9th can be celebrated among friends and family. Because you have already celebrated your birthday on May 9th, no one will ask you whether you will do it when you are sixty. Doing it twice in one birthday is also a decent thing for the elderly. Why not?