Most orthotics wear out in 2 to 3 years. The majority of my clients that come back in 2 to 3 years is because they can feel the original symptoms beginning to return as the orthotic wears out.
Having said that, I see clients that have orthotics that are 10 to 15 years old and they are very happy with them as they are.
Do flat feet need to be treated? Why or why not?
Nope. Flat feet is not a disease. If you are pain-free, there is nothing to treat.