Federal education loans are not subject to the "defense of infancy", so you can be younger than 18 and still sign the promissory note to obtain a federal education loan.

The Free Application for Federal Student Aid (FAFSA) does not have any age restrictions. You can submit it even if you are still a minor.

For private student loans it depends on the age of majority, which varies from state to state. In most states it is age 18, but in a handful of states it is higher. Pennsylvania is one of the states where the age of majority is 18.