Answer:
The line a runner strives to reach
Longer than a decade and shorter than a milennium
I can be as thin as a picture frame but my insides have many things you can see.
Every country has one, though we are not the same. Waving to our citizens, throughout the wind and rain. What is it?
It is a symphony of noise, It can produce both grief and joys, It is inspiring and grand, Made by a person or a band.
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.