What to wear to a job interview at Rita's Italian Ice?

I'm 14 years old and I received a call for an interview at Rita's after applying there a while ago. I don't think it is a very formal interview so I'm thinking nice jeans and a conservative shirt will work, but I'm not sure. Will that make me seem unprofessional? I don't want to go overdressed, however, to see that the person interviewing me is casual..