It is very embarrassing for a woman to reveal her age and for a man to disclose his earnings. They would like to keep this to themselves and let's respect that. We don't have to ridicule them for hiding their age or salary. These days it's also better not to ask a woman how much she earns.
Mr. Mohan, "Every woman wants to look younger and she is afraid of looking aged", not every woman wants to look younger, there are women who love to age gracefully and they have carried it very elegantly as well. It's most women want to look younger but not every woman. Again, I think its a bit exaggerated when you have said that women would tell 10 years lesser than her actual age. First, she would be hesitant to reveal her age, even if she does I don't she would reduce it to 10 years than her actual age.
Mr. Sun, what makes you say that only an old lady with makeup would feel shy to reveal her age? Let me tell you a real incident, I once called up my friend and talked with her daughter who was hardly 5 years old. So, to start the conversation, I asked her how old are you dear one, and you know what she said- Don't you know you shouldn't ask a girl her age?
So, as per your comment was she not a gentlewoman or rather a child? So I think that's not right to categorize that only old women will not reveal her age.
Unless it's official why should we poke our nose to know other's age or salary, be it a man or women?