Treatment of teenagers without parent present

I am a senior nursing student. In my leadership/management class we got into a discussion of what age a teenager can be seen in a family practice doctor office without a parent present. What age does your practice allow a teenager to be seen without a parent or guardian present?

I spoke for age 16, do to most states allow a 16 year old to drive, so obviously if they have a license they could go to a doctor for a cold, or rash. I know that my local doctor's office allows teens to be seen without an adult as long as there is not any consent forms that need to be signed for vaccines, or procedures such as mole removals.

Thanks!!!
Patricia