Yes, some time ago, Florida did away with any state enforcement of wage and hour, including the restrictions on working students on school nights. You know, all that "reduce the size of government, tighten our belts instead of raising taxes" in play there.
What becomes a trend anywhere and any time there is a recession, (so that there is a good sized pool of labor begging for work to support themselves on) is that the employers hire part-time student workers instead of full time regular workers who are trying to live and perhaps even support a family on their wages. These part time students require no benefits, don't beg for more hours.
Then they give them far too many hours and work them far into the night. Teachers complain that their older high school students are falling asleep at school because they are closing down restaurants at 2:00am and trying to stay awake at school that same morning. So the legislature a few years back enacted some guidelines pertaining to school age workers. The problem is, there are no teeth in this law, and without a state Wage and Hour program, there is no enforcement of it.
It was up to you, the parent to decide that your son was working too many hours, and it was interfering with his school work. But he was not fired illegally, or for discrimination based on his age.
He was fired because he said he couldn't do exactly what they asked as far as hours, and they don't give a care, and can fire him at will and come up with someone else who may not complain. This is an excellent learning for him about why he wants to stay in school and get a better job later, so he will not aways be at the mercy of these types of employers.
Maybe he'll be able to find another job with another employer who's not breaking the law.