What shall I visit at East coast of North America within 6 nights?

You can't rent a car unless you're 25 but maybe you could take a train or bus around? I'm not sure. And go to Philadelphia I love it there! And if you want to go south you can go to beaches in North Carolina and FLORIDA (where I live). Tennessee is really pretty and nature-y if you're into that. Florida has palm trees and beaches and if you're interested in American culture you can go to Miami and see how different it is from the north (more multi cultural a lot of Hispanic people) . You can go to Ocean City in New Jersey or Maryland( there are two) and see the boardwalks and stuff. Good luck!