For example, it is probably the case that a 15 year old cannot work more than 2 or 3 hours on a school day and they may not be able to work after 7pm or even sundown depending on state laws. The DOL has rather strict rules about when a minor is actually an intern vs an employee. If you are thinking of not paying this minor I would think again as the ramifications could be catastrophic.
The DOL has 6 tests. Fail one and your minor is an employee and you had better be paying them at least minimum wage. These are the ones you are likely going to run a foul of:
1) The internship, is similar to training that would be given in an educational environment
2) The internship experience is for the benefit of the intern;
3) The employer shall derive no immediate advantage from the activities of the intern, and on occasion, its operations may actually be impeded
In any case, enforcing age based job restrictions remotely is not feasible and I would thank the individual and encourage them to reach out to you when they turned 18.