First things first -- retain counsel to assist you. I presume that because you are pointing out that you are now 18, the delinquent act with which you are charged occured when you were 17 years old. Your attorney will be able to let you know how you will be treated.
In no way am I offering you legal advice, and in no way has my comment created an attorney-client relationship. You are not to rely upon my note above in any way, but insted need to sit down with counsel and share all relevant facts before receiving fully-informed legal advice. If you want to be completely sure of your rights, you must sit down with an experienced criminal defense attorney to be fully aware of your rights.
Assault 4, is a class A misdemeanor and carries a penalty of up to 365 days in jail and/or a fine of up to $500.00 plus court costs of about $135.00 AS AN ADULT. I assume from your post you were a juvenile when charged. I further assume you have retained a criminal defense attorney in your area, if not, do so ASAP. The prosecutor will review the facts with the police and the prosecuting witness(s), review your prior juvenile court contacts/record and speak with your attorney about you side of the case. Options include informal adjustment, an admission, a sentence to serve in a juvenile facility, volunteer hours to perform, counseling, etc. depending on the facts, or a trial by the judge.
I am trying to give you a general answer to your question. We do not have an attorney-client relationship by this response on the avvo website. I have not been retained to represent you. I am licensed to practice law in Kentucky and in federal court in this state and the Southern District of Indiana. You need to seek legal advice from an attorney licensed to practice in your area..