I have a flag that is very old looking that have Valley Forge Co stamped on it with black ink. It has the words Spring Penn and another stamped number I think. It was purchased at a estate sale. It has the first star with double blue cloth sewed and the entire flag is sewed together. The person at the estate sale said it belonged to her 96 year old grandfather who was in the army. How do you determine the age of this flag? Is it a collectible?