Hard to tell people have been doing things with shell from the beginning of man til modern man. So some context of where found,or if found with other items ,they could help to put an approximate date when the shell was used for the jewelry. Like if you said it was from a Native American site I would suggest older but if in an R.V. park I would think modern (hippie)type era but shells are not easy to drill, I know I have used in some art projects I have done, You need patience with them.