According to USA Today, persons under the age of 18 are prohibited by law from renting cars because they are not permitted to enter into contracts. Past the age of 18, each agency sets its own age restriction.
New York and Michigan require rental agencies to rent to customers who are 18 years or older, while the remaining 48 states leave this decision up to the agencies, states USA Today. Many agencies set 25 as the minimum age, while others impose an additional surcharge to drivers under this age. The minimum age also varies between different locations of the same rental agency.