If you mean it is rude to ask a person things like how old they are when you have only just met, it's "Asking such things on first acquaintance is kind of rude here in my country."
Thank you and I am sorry about bothering you a lot, but how about 'at /on our first meeting'? I think we also can say, " At our first meeting (On our first meeting) , they asked some rude questions." What do you think? Thank you so much in advance.