This is an interesting question. I think.
We all know that in English speaking countries, asking lady's age is impolite. But in Chinese culture, it's not a secret. However, the thing is, if you are an English native speaker and ask my age, maybe I will still think it's offensive, because I know that in your culture.
Then, how about other culture and countries, such as Spanish speaking countries, islamic countries and so on? I want to ask this because I met someone on this website from an islamic country who asked my age at the first time, which was soooo strange. But I do not know much about his culture, so I told him my age, since in China age is not a secret. I also have a friend from a Spanish speaking country who asked my age when we practiced speaking. But at that time, we are already language partners so it seemed quite normal, at least in Chinese point of view.
So, is people's age private in your culture? Or is only the lady's age a secret rather than that of men?
Cannot expect more than your reply and answer.