It's acceptable that you choose who you wish to speak to. Fair? That's asking for an opinion as there is no right or wrong with these kinds of things. Many people don't want others to know their age for many reasons. They don't want to be prejudged on the basis of age, they don't want to be excluded on the basis of age, or they just feel that their age is private & should remain that way. I know my mother tells people that she's 39 and has done so for decades. She knows it's a joke but her age is her business.