I thought 60s too. I believe that bow at the front is a very 1960s trend, and with a high waist too.
Could be a wedding dress.
I believe that in earlier periods, wedding dresses tended to cover more flesh, meaning they'd have sleeves and wouldn't be very low cut, because they were usually worn in church, of course, and it was normal to dress modestly in church. At some point this became less important, and you start to get sleeveless and more revealing wedding dresses. I don't know exactly this change started. I'm sure it wasn't an overnight thing, and would vary from place to place, family to family, wedding to wedding, religion to religion, etc.