I have experienced the same thing and when people ask for your age it is generally because they are impressed and not because they think you can't be taken seri

I have experienced the same thing and when people ask for your age it is generally because they are impressed and not because they think you can't be taken seriously. And regarding pay, if you know what you want then you can't control what they will offer you, you can say what you want and require and then either decline or accept the offer :)