Students can apply for student loans without their parents cosigning at any point they are ready to enter college even if they are under the age of 18. This is because the "defense of infancy" does not apply to federal student loans.
The "defense of infancy" is a law that presumes minors cannot enter into legally binding contracts and considers any such contract as void. Therefore, a minor cannot apply for a personal loan, an apartment, a car loan, or any other contract that is legally binding. However, the Higher Education Act explicitly excludes federal student loans from this defense. If you enter into a contract for a federal student loan without your parents as cosigners, they are not responsible for your loan.