You can ask your parents or brother and sister or even your close relatives to have line application and get Iphone 6 at your behalf.
As a rule, minor/minority could not enter into contract. Since, plan subscription is a contract, your application will be disapproved on such ground.
I suggest, your parent or guardian, provided they meet the qualification may apply a postpaid plan for you. Once approved, just have a your name indicated as authorized person.
Once, you reached the age of majority and with possible proof of financial capacity, the listed subscriber may request for change of ownership into your name.