Tell the staffing agency your circumstances, and ask them what the company policy is, or what they suggest.
Job descriptions are just what the commpany is looking for. They will hire whoever they feel is the closest match.
Try to be confident, and assertive, without being overbearing or anxious.
I have done a lot of job hunting, and if you really want this job, tell them that. And it would help to tell them why you think you are the right one. Best wishes.