Age - A Sensitive Issue?

Everyone has one....everyone is ageing with every passing minute. Everyone was one young and most people get to be old. Scientifically speaking, the yearly age that we count is only the 'approximate' age of our bodies. I heard some scientist have done a research in which the age of a body is actually determine by the condition of out internal organs and systems. For instance, if someone has lived for 35 years, their body might be younger or older than 35 years, depending on how it has been taken care of. Therefore, age...is an approximation anyway! So why do people take offence when asked how old they are? Why is it considered impolite or rude? Is it fear of approaching death? What is it?