Ringlets 1840s-early 60s but it did vary depending on whether older women thought they suited them or not...I've got a mid-late 60s photo of a woman in her 30s wearing some very dire looking ringlets - looks like a drowned rat!

I'm going mid-late 60s for the photo because the skirt is still very full but simple in comparison to anything from the 1870s; the hairstyle is typical 1860s, and the fact that the hair is completely above/behind the ears suggests it's not early 60s.