I keep coming back to look at this lovely dress, mostly because I adore the fabric. My first thoughts were it was an antique dress circa 'Teens era that was altered and I still feel that is a strong possibility, especially due to the shorter length. As Jonathan mentioned, you would not generally see an A & C fabric used in clothing after the early 1920s. The loose style and those wonderful front panels (do they float?) and shorter length look more mid 1920s.
Someone could have found the unused fabric and loved it, or found an antique dress and loved the fabric, so took it apart to make up a home made dress in the mid 1920s. If so, the fabric itself could be even older, perhaps going back to 1900.
The fabric looks like a cotton or linen. It might be a hand block printed fabric, or it could be screen printed. Either method adds to the charm and rarity. I think it is a very special dress.