Rental car laws vary from state to state, so it is important to understand the laws that apply to the state you are planning to visit and rent your car in.
It almost goes without saying that all drivers who will be driving the rental car will need a valid driver's license. This does not include learner's permits. Foreign nationals may use their international driver's license, if they have one. If you wish to use your license from your home country, you will most likely also need to produce your passport and additional identification. Make sure to check with the rental company before you arrive in order to make sure you bring what you need.
In New York, anyone over the age of 18 may rent a car, as long as they have a valid driver's license and insurance. Any extra costs for insuring you as a younger driver may be passed to you in the price of the rental itself as car rental companies are permitted to charge different rates depending on the age of the person renting the car.
Car rental companies in New York cannot require you to have a credit card as a condition of renting to you. However, keep in mind that if you do not have a credit card they are permitted to screen you, a process that can take several days. If you do not have a credit card, it is a good idea to call the rental company a few days before you rent so that you can start this process in time to get your car when you need it. In addition, you will be required to put down a refundable security deposit in cash before renting, similar to a security deposit that would be charged on your credit card.
If you are visiting New York from another country, please keep in mind that traffic laws can vary greatly from state to state. This includes speed limits and consequences for violating them. There are no check points at borders between states, so it is not always easy to tell when you have crossed into another state.
Remember that you will be responsible for any traffic tickets or parking tickets you receive on your rental car. Parking on city streets, especially in New York City, can have complicated regulations about which side of the street you are allowed to park on on which days and what times. These regulations are clearly posted on street signs, so just be aware of them when parking and you should have no problems.