I am not licensed to practice law in Florida so the following should not be taken as legal advice, but simply as information based on general principles of law which is intended to educate. If you need legal advice, please consult a lawyer who holds Florida licensure.
The rules governing the condo you are renting will be found in three different places: (1) the Declaration of Condominium, (2) the deed to the condominium you are renting, and (3) the bylaws of the condominium association. (1) and (2) will have been recorded in the municipal land records. (3) will be at the condominium association's office and you may be able to stop by and have a look at them. Most likely the restriction is in the bylaws.
To amplify, the restriction you describe is one which the governance structure of the condominium complex is free to adopt. If they've adopted it, that's the rule. I know of no principle of law that says the condo owners' association cannot adopt the occupancy limits on renters you describe.