I am not a licensed Florida attorney; however, in most states a parent has an obligation to continue paying child support until the child is "emancipated." This means that as long as he is still a full-time student (even through college), you will have to continue paying. Alternatively, if your son discontinues his full-time education after he is 18, your chances of terminating your support obligation will be much greater if you make the appropriate application to the court.
Child support terminates when the child turns 18. Depending on the terms of your divorce decree (if you have one), you may need to continue paying for certain other expenses outlined in the order.
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.