Are eighteen year olds ready make decisions on their own and be independent?

Are eighteen year olds ready make decisions on their own and be independent? As a parent of a child off to the University, I have had to confront this question. At the orientation I was make acutely aware, the staff at the University “Your child is an adult. You do not have any right to their documents, medical records etc;”. Incidentally when it comes to paying for college, the parents are still kind of responsible!
So, are eighteen year olds really equipped emotionally to make decisions and be independent? My experience is that it depends on the child. Some children are well grounded and mature and can make decisions. But not all children are ready. What are the consequences when society decides to give all eighteen year olds the status of adults – even those that are not ready to handle the independence? Unfortunately, I suppose there is no way to apply different standards to the two groups in a university setting. I am sure the staff will tell you that all students need this independence (irrespective of their level of maturity) to explore the various aspects of life and that they will all step up to the challenges.
I only hope that this is indeed the case!