blubirdboutique, I agree that the beads look older - you can see irregularity in their shape that shows they're not modern. I've seen beads like these many times on '20s dresses but the panel could be from an earlier garment.
The way the beads on the panel go beneath the waist seam show that this is not the original design - the panel has been repurposed into the top. It's nicely made, but the construction techniques (especially with the armhole opening) do not look as old as '20s to me, more like the '40s-50s or perhaps even more modern but the fastenings look older.
You can see the press studs on the inside of the neckline, suggesting that they might have supported a removable collar at some point.
It's a lovely piece, I'm sure that if I could hold it, I'd get a much better idea of age, as certain details are hard to convey in photos.