Kiwi Rental Cars

Do you have a driving license for at least 1 year?

OK, then look here for age restrictions:-

The driver must have held a full driving licence for at least one year. At STEP2, click on the link "IMPORTANT INFORMATION' displayed to the right of the car photo of your choice. This will open another smaller window and if you click on "DRIVER" you will see what age restrictions there may be and any associated fees. Try a few different car models / suppliers, as they do differ. For example, Thrifty say this about age:-

Driver's age 25 to 99 years. Young driver's age: 21 to 24 years. Charge 11.5 NZD per day. Includes 15% tax Customers who fall outside the age limitations will not be able to hire a car unless there is a young or senior driver fee specified in this section. Please note that if applicable, this fee will be included in the rental price and will be payable on arrival at the rental desk in the local currency.