I am 16 and I want to buy a car without a contract.

Any time you buy something, that's a contract.  YOu and the other parties to the agreement have agreed that you will pay a certain price and in return the other party will give you title to some property.  There are likely going to be other terms as well.  While the adult with whom you contract is bound by it, you, since you are a minor, have the right to revoke that contract, meaning that any party you deal with would face the risk that 3 weeks after you reached agreement, you can find another car for cheaper, or lose your job, or for whatever reason change your mind and rescind the contract.  Nobaody wants to take that risk, and so they will require a competent adult as a contracting party.