Parents: why do you always say this?

It is just a difference in perspective. It is hard to explain when you are an adult - remember, we have been 16, and we remember a lot of it, but you have not been 30-something or 40-something. So give your parents the benefit of the doubt. There are ways you are getting mature and need and deserve more responsibility, and there are ways you are less mature and not ready for certain things. It is parent perspective. Here is another one you have heard before I bet: you'll understand when you are older. :)