Whether or not your juvenile record will affect employment is up to the agency making the hiring decision. As a general rule, people with no criminal history are at an advantage when seeking law enforcement work.

You should seek expungement of your record as soon as you qualify - in simple terms, five years from final discharge or, since you're over 18, at any time if the prosecutor concurs. (Depending on the full facts the waiting period could be shorter than five years.)