Can I hit someone first in a fight if....?

Pushing qualifies under the law as ault. If there was physical contact prior to you throwing the punch then he will share part of the blame for the confrontation. Based on your description it sounds like you're a minor so the worst that's likely to happen is you'll both be charged with misdemeanor ault and sentenced to community service. If your family is well to do then you can get a lawyer to petition the court to have your records sealed once you turn 18.