Yes, it is more than OK. Players are encouraged to become referees. It can even help them to become better players!
The Player Referee Organization (PRO) is a program designed to help teenage players become a referee. PRO referees are provided training, mentoring, and opportunities to challenge themselves. Teenage referees gain a variety of benefits from being a referee, including self-confidence, assertiveness, problem-solving skills and increased communication abilities. The training and time refereeing games can also earn them community service points, as AYSO is a non-profit, volunteer, community organization.