There are frum Jews on nearly every flight from NY to FL. If you otherwise feel comfortable having them fly by themselves, be at the check-in area early, try to find a family that doesn't mind to take them under their wing (for the purposes of fulfilling the guardian requirement)
I've been approached once by a parent asking if I agreed to be the guardian for their 14 & 16 year old traveling on my flight from NY to FL as the airline wanted to charge them a hefty unaccompanied minor fee. ( A 16 y/o may travel solo but cannot serve as guardian for a child under the age of 16 - at least those were the terms of that airline, at that time)
I did it gladly. Everything went smoothly; I even got a ride from the airport with whoever came to pick them up.