Really nothing to worry about. A person can take flying lessons at an age but cannot fly solo (without an instructor onboard) unless at least 16 in a powered plane or 14 in a glider. An instructor spends many hours with a student both in the air and on the ground in personalized instructions. A student also spends many hours in a Ground School classroom, doing homework, taking practice tests, etc.
Main reason a teenager flying alone is not a problem is there are one or more very experienced pilots called Certificated Flight Instructors that ensure the student is more than qualified for solo flight, long cross-country solo flights, and eventually their practical flight test with a Designated Pilot Examiner who is a representative or an employee of the FAA.
If any of these adults have any question about the mental or physical capabilities or emotional maturity of a flight student of any age, the student is grounded or solo flight is delayed until after these issues are resolved. In addition, some Flight Schools and programs require letters of reference from unrelated adults such as teachers.
The FAA requires at least 40 hours of dual instruction and solo flight experience before they can take the flight test, among other requirements. The national average of such logged time is reported at around 67 hours. Although not a CFI, I have mentored many flight students toward their license and have flown with each one after they received it, and have never had a moment of concern. So in my opinion, a teen flying a plane is not a concern since so many controls are in place. Fail one and they don't fly solo or at all.
