Hmm. This dress is indeed a bit confusing.
The print looks more modern than the 1960's to me. If I saw that print not as a part of this dress, my first guess would be 1980's. The dress also seems pretty long and the actual hem pretty narrow for a 1960's frock. The style of the bodice has a 50's/60's to me though, with the exception of the dipped front waistline.
I am assuming it is home made? Are the seams cut with pinking shears by chance? What are the measurements (bust, waist, length)?
My initial guess is that the dress is from the 1980's. The print, apparent length, narrow hem, nylon zipper, dipped waistline all steer me in this direction.