Need a second opinion. should all flat feet teens wear supportive insoles even if no symptoms?

No: Orthotics are purely for comfort. They will not change development of the feet. If they are comfortable and make the patients feet or lower extremities feel better, then they are useful. They are not "necessary" for asymptomatic teens.

Depends: Teens with flat feet may not complain of pain because they are so flexible however when start playing organized sports they can become more symptomatic. It also depends on the parents. If they have foot problems then it is most likely will affect their kids. The supports can only help by supporting the bones, tendons, and ligaments while the foot matures just like braces for teeth.