I used chabads at enterprise at jfk and had no problem. I had a avis code for under 21 as well. Rented cars in new york from the age of 18
There are very little awd out there that wave the fee and dont make you show id. If to many people use them it will be shut down, so it will most prob not be posted.
WARNING netjet will not work anymore. You will get a good rate online, but at the station they will wait for you or charge you the full rate on return. Its on FT so dont use anymore