K.K.
My stepdad is actually a college financial planner and I work with him so I know a good deal about this stuff. The FAFSA (free application for student aid) can be filed on January 1 of the student's senior year in high school for next year in college. What you want to do is fill it out based on an estimate of your income (since you won't have your taxes done yet) and then go back and update it once your taxes are complete. However, since you have waited, your taxes are probably done so just head on over to the FAFSA website (fafsa.gov) and fill it out so the school(s) your son is applying to are alerted that he is seeking financial aid. Then you have to go to the FL state aid website and fill out that application so your son is considered for state aid (if he is going to an in state school).
Just be sure you fill the forms out correctly because a good majority of people fill them out wrong and can end up paying more for their children's education than they should have.