Question on H and R blocks Refund Anticipation Loan?

I am planning on going to Hand R block tommorow and getting my taxes done and i am just wondering if everyone is approved for the Refund Anticipation Loan where you get the money on the same day or did you have to have a certain credit rating ect.... I am just wondering cause i am 18 years old and dont have any credit built up but i dont know how they do all that .