@KristinWard,
I don't know what the law is in Florida, but under federal law age is not a protected category, except for hiring claims under the ADA, where it's older job applicants who are protected, not younger ones. So, unless Florida has some additional protections for renters based on their age, I don't see how this guy has a case. Of course, since you own a number of rental properties, you should have a lawyer on retainer who can assist you in these kinds of matters. I suggest you call him/her.