21 the same as anywhere else in the states. However, if you re between the ages 21-24 you may be charged an extra $20 a day. I don t really know why but that s just how it is.Hope this helped :]
Go to the websites of Avis, Enterprise or Hertz, and type in the location of where you ll be visiting in Hawaii, they will be able to tell you their minimum age to be able to rent a car.
most places you will have to be 24. very few will go for 21. good idea tho if you want to really get around on vacation and not waste time waiting for the bus