Question about assistant manager job?

I started working at a fast food place when I had just turned 16, I'm now 17 (about to be 18 in september) and was promoted to shift leader a few months ago. They are now planning on promoting me to assistant manager (I am VERY into the whole managment thing. I want to go to college for like managment in hospitality and business) so I definitly want to take this oppertunity. I live in Florida. I just want to know if it is legal for me to have the title of assistant manager yet, since im not 18 yet. Or is it just most places probably prefer 18 and over for obvious reasons? Like is it an actual law? I do online school just so you know.