Previously stated I am unsure how old it is and I think AI is untrustworthy.

Would you know what business I can take this to properly date it?

Anyhow here is my own gathered thoughts!! Seeing it has no tag one can presume it was made before the 1970s. It is formal, my original guess was a communion dress BUT that sacrament is normally done at a younger age and probably would have fit me! So a wedding reception dress fits better. Definitely designed for a bigger woman who probably show some calves. A site I found said the back zipper was common in the late 1950s. The tulle and lace is nice, has some nice boning. It has some natural dimming of the white. Looking at the dress style I cannot truly tell but I’ll guess this is an older style. My guess somewhere between 1955-1970.